Stockholm, Sweden

The Royal Institute of Technology is a university in Stockholm, Sweden. KTH was founded in 1827 as Sweden's first polytechnic and is one of Scandinavia's largest institutions of higher education in technology. KTH accounts for one-third of Sweden's technical research and engineering education capacity at university level. KTH offers programmes leading to a Master of Architecture, Master of Science in Engineering, Bachelor of Science in Engineering, Bachelor of Science, Master of Science, licentiate or doctoral degree. The university also offers a technical preparatory programme for non-scientists and further education.There are a total of just over 14 000 full-year equivalent undergraduate students, more than 1700 active postgraduate students and 4600 full-time-equivalent employees. KTH is one of the leading technical universities in Europe and highly respected worldwide, especially in the domains of technology and natural science. Wikipedia.


Time filter

Source Type

Zelenina M.,Karolinska Institutet | Zelenina M.,KTH Royal Institute of Technology
Neurochemistry International | Year: 2010

Three aquaporins are expressed in the brain. AQP4, the predominant brain water channel, is expressed in astrocyte endfeet facing brain capillaries, perisynaptic spaces, and nodes of Ranvier. It is implicated in brain edema formation and resolution. It is also believed to assist clearance of K+ released during neuronal activity. AQP1 is expressed in epithelial cells of choroid plexus and is implicated in cerebrospinal fluid formation. AQP9, which has been reported to be present in astrocytes and in subpopulations of neurons, is implicated in the brain energy metabolism. All three brain AQPs are strongly upregulated in brain tumors and in injured brain tissue.Water and solute transport via AQPs depends on concentration gradients across the membrane, but the magnitude of the transport is to a large extent determined by the single channel permeability of AQPs and by their abundance in the cell membrane. The future therapies will have to address not only the forces driving the water and solute transport (e.g. as mannitol infusion does in the treatment of brain edema), but also the regulation of AQPs, which provide the means for water entry to the brain, for water exit from the brain, and for redistribution of water and solutes within the brain compartments. This review summarizes the data concerning structure, permeability, role in the brain, short-term and long-term regulation of the three AQPs. © 2010 Elsevier Ltd.


Kumar M.,KTH Royal Institute of Technology | Persson C.,KTH Royal Institute of Technology | Persson C.,University of Oslo
Applied Physics Letters | Year: 2013

Cu3BiS3 is a potential photovoltaic material. Employing a first-principles approach, we calculate the structural, electronic, and optical properties of Cu3BiS3, and we demonstrate that Cu3BiS3 is an indirect band gap semiconductor in contrast to similar chalcogenide semiconductors. The fundamental band gap energy is estimated to be Eg ≈ 1.5-1.7 eV. The analysis reveals that Cu 3BiS3 has a much stronger absorption coefficient (>105 cm-1) compared to other Cu-S based materials like CuInS2 and Cu2ZnSnS4. This is explained by the presence of localized Bi 6p states in the band gap region, generating a flat lowest conduction band. © 2013 American Institute of Physics.


McInnes B.,KTH Royal Institute of Technology | McInnes B.,National University of Singapore
Classical and Quantum Gravity | Year: 2014

Future facilities such as FAIR and NICA are expected to produce collisions of heavy ions generating quark-gluon plasmas (QGPs) with large values of the quark chemical potential; peripheral collisions in such experiments will also lead to large values of the angular momentum density, associated with the internal shearing motion of the plasma. It is well known that shearing motions in fluids can lead to instabilities which cause a transition from laminar to turbulent flow, and such instabilities in the QGP have recently attracted some attention. We set up a holographic model of this situation by constructing a gravitational dual system exhibiting an instability which is indeed triggered by shearing angular momentum in the bulk. We show that holography indicates that the transition to an unstable fluid happens more quickly as one scans across the quark matter phase diagram towards large values of the chemical potential. This may have negative consequences for the observability of quark polarization effects. © 2014 IOP Publishing Ltd.


Jimenez J.B.,Leuven University | Koivisto T.S.,University of Oslo | Koivisto T.S.,KTH Royal Institute of Technology
Classical and Quantum Gravity | Year: 2014

In this paper we consider an extended Gauss-Bonnet gravity theory in arbitrary dimensions and in a space provided with a Weyl connection, which is torsion-free but non-metric-compatible, the non-metricity tensor being determined by a vector field. The action considered consists of the usual Einstein-Hilbert action plus all the terms quadratic in the curvature that reduce to the usual Gauss-Bonnet term for vanishing Weyl connection, i.e., when only the Levi-Civita part of the connection is present. We expand the action in terms of Riemannian quantities and obtain vector-tensor theories. We find that all the free parameters only appear in the kinetic term of the vector field, so two branches are possible: one with a propagating vector field and another one where the vector field does not propagate. We focus on the propagating case. We find that in four dimensions, the theory is equivalent to Einstein's gravity plus a Proca field. This field is naturally decoupled from matter, so it represents a natural dark matter candidate. Also for d = 4, we discuss a non-trivial cubic term in the curvature that can be constructed without spoiling the second-order nature of the field equations, because it leads to the vector-tensor Horndeski interaction. In arbitrary dimensions, the theory becomes more involved. We show that, even though the vector field presents kinetic interactions which do not have symmetry, there are no additional propagating degrees of freedom with respect to the usual massive case. We show that, interestingly, this relies on the fact that the corresponding Stückelberg field belongs to a specific class within the general Horndeski theories. Finally, since Weyl geometries provide the natural ground on which to build scale invariant theories, we apply the usual Weyl gauging in order to make the Horndeski action locally scale invariant, and discuss new terms that can be added. © 2014 IOP Publishing Ltd.


Silaev M.,KTH Royal Institute of Technology | Silaev M.,RAS Institute for Physics of Microstructures | Babaev E.,KTH Royal Institute of Technology | Babaev E.,University of Massachusetts Amherst
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We report a microscopic derivation of two-component Ginzburg-Landau (GL) field theory and the conditions of its validity in two-band superconductors. We also investigate the conditions when microscopically derived or phenomenological GL models fail and one should resort to a microscopic description. We show that besides being directly applicable at elevated temperatures, a version of a minimal two-component GL theory in certain cases also gives an accurate description of certain aspects of a two-band system, even substantially far from T c. This shows that a two-component GL model can be used for addressing a wide range of questions in multiband systems, in particular vortex physics and magnetic response. We also argue that a single Ginzburg-Landau parameter cannot in general characterize the magnetic response of multiband systems. © 2012 American Physical Society.


Bagherbandi M.,KTH Royal Institute of Technology | Bagherbandi M.,University of Gävle | Sjoberg L.E.,KTH Royal Institute of Technology
Physics of the Earth and Planetary Interiors | Year: 2012

The crustal thickness can be determined based on gravimetric-isostatic and seismic models. Modelling crustal thickness by a gravimetric-isostatic model suffers from some problems. The isostatic assumption for compensating the topographic potential is incomplete, as there are other effects which should be considered. Using the isostatic hypothesis for determining the depth of crust causes some disturbing signals, non-isostatic effects. , which influence the crustal thickness determination. Isostatic and non-isostatic compensations are the main issues in this paper. We present three methods to overcome the problem due to the disturbing signals, namely the approach by truncating the spherical harmonic approach, determination of non-isostatic correction using a seismic crustal thickness model (e.g., CRUST2.0) and combination of isostatic and seismic models by applying a least-squares adjustment method. The estimated results of the non-isostatic effects varies between -65.2 and 391.8. mGal in Fennoscandia. The root mean squares difference of the crustal thickness obtained from the gravimetric-isostatic model and CRUST2.0 is improved up to six times (from 6.15 to 0.97. km) when the non-isostatic effects are considered. © 2012 Elsevier B.V..


Solomon A.R.,University of Cambridge | Akrami Y.,University of Oslo | Koivisto T.S.,KTH Royal Institute of Technology
Journal of Cosmology and Astroparticle Physics | Year: 2014

The ghost-free theory of massive gravity with two dynamical metrics has been shown to produce viable cosmological expansion, where the late-time acceleration of the Universe is due to the finite range of the gravitational interaction rather than a nonzero cosmological constant. Here the cosmological perturbations are studied in this theory. The full perturbation equations are presented in a general gauge and analyzed, focusing on subhorizon scales in the quasistatic limit during the matter-dominated era. An evolution equation for the matter inhomogeneities and the parameters quantifying the deviations from general relativistic structure formation are expressed in terms of five functions whose forms are determined directly by the coupling parameters in the theory. The evolution equation has a similar structure to Horndeski-type scalar-tensor theories, exhibiting a modified growth rate and scale-dependence at intermediate wavenumbers. Predictions of the theory are confronted with observational data on both background expansion and large-scale structure, although care must be taken to ensure a model is stable. It is found that while the stable models fit the data well, they feature deviations from the standard cosmology that could be detected or ruled out by near-future experiments. © 2014 IOP Publishing Ltd and Sissa Medialab srl .


Jia T.,KTH Royal Institute of Technology | Jiang B.,University of Gävle
Physica A: Statistical Mechanics and its Applications | Year: 2012

From a complex network perspective, this study sets out two aims around the US airport network (USAN) which is built from en-route location information of domestic flights in the US. First, we analyze the structural properties of the USAN with respect to its binary and weighted graphs, and second we explore the airport patterns, which have wide-ranging implications. Results from the two graphs indicate the following. (1) The USAN exhibits scale-free, small-world and disassortative mixing properties, which are consistent with the mainstream perspectives. Besides, we find (2) a remarkable power relationship between the structural measurements in the binary graph and the traffic measurements in the weighted counterpart, namely degree versus capacity and attraction versus volume. On the other hand, investigation of the airport patterns suggests (3) that all the airports can be classified into four categories based on multiple network metrics, which shows a complete typology of the airports. And it further indicates (4) that there is a subtle relationship between the airport traffic and the geographical constraints as well as the regional socioeconomic indicators. © 2012 Elsevier B.V. All rights reserved.


McInnes B.,National University of Singapore | Ong Y.C.,KTH Royal Institute of Technology
Nuclear Physics B | Year: 2015

Holographic duality relates two radically different kinds of theory: one with gravity, one without. The very existence of such an equivalence imposes strong consistency conditions which are, in the nature of the case, hard to satisfy. Recently a particularly deep condition of this kind, relating the minimum of a probe brane action to a gravitational bulk action (in a Euclidean formulation), has been recognized; and the question arises as to the circumstances under which it, and its Lorentzian counterpart, is satisfied. We discuss the fact that there are physically interesting situations in which one or both versions might, in principle, not be satisfied. These arise in two distinct circumstances: first, when the bulk is not an Einstein manifold and, second, in the presence of angular momentum. Focusing on the application of holography to the quark-gluon plasma (of the various forms arising in the early Universe and in heavy-ion collisions), we find that these potential violations never actually occur. This suggests that the consistency condition is a "law of physics" expressing a particular aspect of holography. © 2015 .


Van Hertem D.,KTH Royal Institute of Technology | Ghandhari M.,KTH Royal Institute of Technology
Renewable and Sustainable Energy Reviews | Year: 2010

For many, the supergrid is seen as the solution that allows the massive integration of renewable energy sources in the European power system. It connects different remote energy sources to the existing grid while offering additional control. It offers balancing through geographic spread and allows a more diversified energy portfolio. In the meanwhile it increases the security of supply. However, technical limitations exist, and it is not yet possible to construct such a supergrid. Several outstanding issues need to be solved. This paper first describes the potential and need for a supergrid. The paper focuses on a meshed, multi-terminal VSC HVDC, and it is explained why this relatively new technology is believed to be the best suitable one for such a grid. The different difficulties or challenges that still exist are addressed. Not only the remaining technical limitations are addressed, but also the techno-economic, control and operational issues are discussed, as well as some regulatory obstacles. © 2010 Elsevier Ltd. All rights reserved.


Liu J.-Y.,Tianjin University of Technology | Zhou S.,KTH Royal Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Motivated by recent measurements of a relatively large θ13 in the Daya Bay and RENO reactor neutrino experiments, we carry out a systematic analysis of the hybrid textures of Majorana neutrino mass matrix Mν, which contain one texture zero and two equal nonzero matrix elements. We show that three neutrino masses (m1,m2,m 3) and three leptonic CP-violating phases (δ,ρ,σ) can fully be determined from two neutrino mass-squared differences (δm2,Δm2) and three flavor mixing angles (θ12, θ23,θ13). Out of sixty logically possible patterns of Mν, thirty-nine are found to be compatible with current experimental data at the 3σ level. We demonstrate that the texture zero of Mν is stable against one-loop quantum corrections, while the equality between two independent elements not. Phenomenological implications of Mν for the neutrinoless double-beta decay and leptonic CP violation are discussed, and a realization of the texture zero and equality by means of discrete flavor symmetries is illustrated. © 2013 American Physical Society.


Chua K.J.,National University of Singapore | Chou S.K.,National University of Singapore | Yang W.M.,National University of Singapore | Yan J.,KTH Royal Institute of Technology | Yan J.,Mälardalen University
Applied Energy | Year: 2013

Air conditioning is essential for maintaining thermal comfort in indoor environments, particularly for hot and humid climates. Today, air conditioning, comprising cooling and dehumidification, has become a necessity in commercial and residential buildings and industrial processes. It accounts for a major share of the energy consumption of a building or facility. In tropical climates, the energy consumed by heating, ventilation and air-conditioning (HVAC) can exceed 50% of the total energy consumption of a building. This significant figure is primarily due to the heavy duty placed on cooling technologies to remove both sensible and latent heat loads. Therefore, there is tremendous potential to improve the overall efficiency of the air-conditioning systems in buildings.Based on today's practical technology for cooling, the major components of a chiller plant are (1) compressors, (2) cooling towers, (3) pumps (chilled and cooling water) and (4) fans in air handling units. They all consume mainly electricity to operate. When specifying the kW/R. ton of a plant, there are two levels of monitoring cooling efficiency: (1) at the efficiency of the chiller machines or the compressors which consume a major amount of electricity; and (2) at the overall efficiency of cooling plants which include the cooling towers, pumps for moving coolant (chilled and cooling water) to all air-handling units. Pragmatically, a holistic approach is necessary towards achieving a low energy input per cooling achieved such as 0.6. kW/R. ton cooling or lower by considering all aspects of the cooling plant.In this paper, we present a review of recent innovative cooling technology and strategies that could potentially lower the kW/R. ton of cooling systems - from the existing mean of 0.9. kW/R. ton towards 0.6. kW/R. ton or lower. The paper, broadly divided into three key sections (see Fig. 2), begins with a review of the recent novel devices that enhances the energy efficiency of cooling systems at the component level. This is followed by a review of innovative cooling systems designs that reduces energy use for air conditioning. Lastly, the paper presents recent developments in intelligent air-control strategies and smart chiller sequencing methodologies that reduce the primary energy utilization for cooling.The energy efficient cooling technology, innovative systems designs, and intelligent control strategies described in the paper have been recently researched or are on-going studies. Several have been implemented on a larger scale and, therefore, are examples of practical solutions that can be readily applied to suit specific needs. © 2012 Elsevier Ltd.


Bagherbandi M.,KTH Royal Institute of Technology | Bagherbandi M.,University of Gävle | Sjoberg L.E.,KTH Royal Institute of Technology
Earth-Science Reviews | Year: 2013

The principle of isostasy is important in different fields of geosciences. Using an isostatic hypothesis for estimating the crustal thickness suffers from the more or less incomplete isostatic model and that the observed gravity anomaly is not only generated by the topographic/isostatic signal but also by non-isostatic effects (NIEs). In most applications of isostatic models the NIEs are disregarded. In this paper, we study how some isostatic models related with Vening Meinez's isostatic hypothesis can be improved by considering the NIE. The isostatic gravity anomaly needs a correction for the NIEs, which varies from as much as 494. mGal to -308. mGal. The result shows that by adding this correction the global crustal thickness estimate improves about 50% with respect to the global model CRUST2.0, i.e. the root mean square differences of the crustal thickness of the best Vening Meinesz type and CRUST2.0 models are 6.9 and 3.2. km before and after improvement, respectively. As a result, a new global model of crustal thickness using Vening Meinesz and CRUST2.0 models is generated. A comparison with an independent African crustal depth model shows an improvement of the new model by 6.8. km vs. CRUST2.0 (i.e. rms differences of 3.0 and 9.8. km, respectively). A comparison between oceanic lithosphere age and the NIEs is discussed in this study, too. One application of this study can be to improve crustal depth in areas where CRUST2.0 data are sparse and bad and to densify the resolution vs. the CRUST2.0 model. Other applications can be used to infer the viscosity of the mantle from the NIEs signal to study various locations around the Earth for understanding complete, over- and under-compensations of the topography. © 2012 Elsevier B.V.


Zhang H.,KTH Royal Institute of Technology | Shen H.,University of Adelaide
IEEE Transactions on Parallel and Distributed Systems | Year: 2010

Geographic routing is an attractive localized routing scheme for wireless sensor networks (WSNs) due to its desirable scalability and efficiency. Maintaining neighborhood information for packet forwarding can achieve a high efficiency in geographic routing, but may not be appropriate for WSNs in highly dynamic scenarios where network topology changes frequently due to nodes mobility and availability. We propose a novel online routing scheme, called Energy-efficient Beaconless Geographic Routing (EBGR), which can provide loop-free, fully stateless, energy-efficient sensor-to-sink routing at a low communication overhead without the help of prior neighborhood knowledge. In EBGR, each node first calculates its ideal next-hop relay position on the straight line toward the sink based on the energy-optimal forwarding distance, and each forwarder selects the neighbor closest to its ideal next-hop relay position as the next-hop relay using the Request-To-Send/Clear-To-Send (RTS/CTS) handshaking mechanism. We establish the lower and upper bounds on hop count and the upper bound on energy consumption under EBGR for sensor-to-sink routing, assuming no packet loss and no failures in greedy forwarding. Moreover, we demonstrate that the expected total energy consumption along a route toward the sink under EBGR approaches to the lower bound with the increase of node deployment density. We also extend EBGR to lossy sensor networks to provide energy-efficient routing in the presence of unreliable communication links. Simulation results show that our scheme significantly outperforms existing protocols in wireless sensor networks with highly dynamic network topologies. © 2006 IEEE.


Begue D.,KTH Royal Institute of Technology | Begue D.,The Oskar Klein Center | Pe'er A.,University College Cork
Astrophysical Journal | Year: 2015

One of the key open question in the study of jets, in general, and jets in gamma-ray bursts (GRBs), in particular, is the magnetization of the outflow. Here we consider the photospheric emission of Poynting-flux-dominated outflows, when the dynamics is mediated by magnetic reconnection. We show that thermal three-particle processes, responsible for the thermalization of the plasma, become inefficient at a radius of rsup ∼ 109.5 cm, far below the photosphere, at ∼1011.5 cm. Conservation of the total photon number above rsup combined with Compton scattering below the photosphere enforces kinetic equilibrium between electrons and photons. This, in turn, leads to an increase in the observed photon temperature, which reaches ≳8 MeV (observed energy) when decoupling the plasma at the photosphere. This result is weakly dependent on the free model parameters. We show that in this case, the expected thermal luminosity is a few percent of the total luminosity, and could therefore be detected. The predicted peak energy is more than an order of magnitude higher than the observed peak energy of most GRBs, which puts strong constraints on the magnetization of these outflows. © 2015. The American Astronomical Society. All rights reserved.


Hosseinzadeh N.,Swinburne University of Technology | Hesamzadeh M.R.,KTH Royal Institute of Technology
IEEE Transactions on Education | Year: 2012

Project-based learning (PBL), a learning environment in which projects drive learning, has been successfully used in various courses in the educational programs of different disciplines. However, concerns have been raised as to the breadth of the content covered and, in particular, whether PBL can be applied to specialized subjects without compromising the coverage of the required technical content. This paper discusses the advantages and drawbacks of using the PBL methodology in teaching specialized subjects in electrical power engineering, based on the authors' reflections and student feedback. The design and delivery of a PBL-based course in power system modeling and analysis is used as an example. It is asserted that proper usage of PBL makes it possible to deliver both technical content and generic professional skills in a specialized course. © 2012 IEEE.


Sanchez-Dominguez M.,CIMAV | Pemartin K.,CIBER ISCIII | Boutonnet M.,KTH Royal Institute of Technology
Current Opinion in Colloid and Interface Science | Year: 2012

In this review, the synthesis of inorganic nanoparticles using oil-in-water (O/W) microemulsions as confined reaction media is discussed. Synthesis using (O/W) microemulsions has been demonstrated for a great variety of inorganic nanoparticles: metallic (Pt, Pd, Rh, Ag), single metal oxides (CeO 2, ZrO 2, TiO 2, Fe 2O 3), mixed and doped metal oxides (Ce 0.5Zr 0.5O 2, Ce 0.99Eu 0.01O 2, Zr 0.99Eu 0.01O 2, and Fe 2Mn 0.5Zn 0.5O 4), semiconductors (PbS, CdS, Ag 2S, ZnS, CdSe, PbSe, Ag 2Se), fluorides (CaF 2, YF 3, NdF 3, PrF 3), phosphates (CePO 4, HoPO 4), and chromates (BaCrO 4 and PbCrO 4). There are two synthetic strategies: 1) the use of oil-in water (O/W) microemulsions, in which the precursor is an ionic salt which is dissolved in the continuous aqueous phase; and 2) use of O/W microemulsions, in which the precursor is an organometallic salt dissolved in the oil droplets of the microemulsion. The latter approach keeps more resemblance to the typical W/O microemulsion reaction method, as it has the greatest level of precursor confinement. © 2012 Elsevier Ltd.


Guruswami V.,Carnegie Mellon University | Hastad J.,KTH Royal Institute of Technology | Kopparty S.,Institute for Advanced Study
IEEE Transactions on Information Theory | Year: 2011

The list-decodability of random linear codes is shown to be as good as that of general random codes. Specifically, for every fixed finite field F q,p, ∈ (0,1 -1/q) and ε > 0 it is proved that with high probability a random linear code C in Fq n of rate (1-Hq(p)-ε can be list decoded from a fraction p of errors with lists of size at most O(1/ε). This also answers a basic open question concerning the existence of highly list-decodable linear codes, showing that a list-size of O (1/ε) suffices to have rate within ε of the information-theoretically optimal rate of 1-Hq(p). The best previously known list-size bound was qO(1/ε) (except in the q =2 case where a list-size bound of O(1/ε) was known). The main technical ingredient in the proof is a strong upper bound on the probability that random vectors chosen from a Hamming ball centered at the origin have too many (more than Ω (ℓ)) vectors from their linear span also belong to the ball. © 2006 IEEE.


Zhu B.,KTH Royal Institute of Technology | Fan L.,KTH Royal Institute of Technology | Fan L.,Tianjin University of Technology | Lund P.,Aalto University
Applied Energy | Year: 2013

Recent scientific and technological advancements have provided a wealth of new information about solid oxide-molten salt composite materials and multifunctional ceria-based nano-composites for advanced fuel cells (NANOCOFC). NANOCOFC is a new approach for designing and developing of multi-functionalities for nanocomposite materials, especially at 300-600 °C. NANOCOFC and low temperature advanced ceramic fuel cells (LTACFCs) are growing as a new promising area of research which can be explored in various ways. The ceria-based composite materials have been developed as competitive electrolyte candidates for low temperature ceramic fuel cells (LTCFCs). In the latest developments, multifunctional materials have been developed by integrating semi- and ion conductors, which have resulted in an emerging insight knowledge concerned with their R&D on single-component electrolyte-free fuel cells (EFFCs) - a breakthrough fuel cell technology. A homogenous component/layer of the semi- and ion conducting materials can realize fuel cell all functions to avoid using three components: anode, electrolyte and cathode, i.e. " three in one" highlighted by Nature Nanotechnology (2011). This report gives a short review and advance knowledge on worldwide activities on the ceria-based composites, emphasizing on the latest semi-ion conductive nanocomposites and applications for new applied energy technologies. It gives an overview to help the audience to get a comprehensive understanding on this new field. © 2013 Elsevier Ltd.


Silaev M.A.,KTH Royal Institute of Technology | Thuneberg E.V.,University of Oulu
Physical Review Letters | Year: 2015

We study the spectrum of fermion states localized within the vortex core of a weak-coupling p-wave superfluid. The low energy spectrum consists of two anomalous branches that generate a large density of states at the locations of the half cores of the vortex. Fermi liquid interactions significantly stretch the vortex structure, which leads to a Lifshitz transition in the effective Fermi surface of the vortex core fermions. We apply the results to the rotational dynamics of vortices in superfluid He-B3 and find an explanation for the observed slow mode. © 2015 American Physical Society.


Wicklein B.,University of Stockholm | Kocjan A.,Jozef Stefan Institute | Salazar-Alvarez G.,University of Stockholm | Salazar-Alvarez G.,KTH Royal Institute of Technology | And 4 more authors.
Nature Nanotechnology | Year: 2015

High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m-1 K-1, which is about half that of expanded polystyrene. At 30°C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials. © 2015 Macmillan Publishers Limited. All rights reserved.


Hebeler K.,Ohio State University | Lattimer J.M.,State University of New York at Stony Brook | Pethick C.J.,Copenhagen University | Pethick C.J.,KTH Royal Institute of Technology | And 2 more authors.
Astrophysical Journal | Year: 2013

Microscopic calculations of neutron matter based on nuclear interactions derived from chiral effective field theory, combined with the recent observation of a 1.97 ± 0.04 M⊙ neutron star, constrain the equation of state of neutron-rich matter at sub- and supranuclear densities. We discuss in detail the allowed equations of state and the impact of our results on the structure of neutron stars, the crust-core transition density, and the nuclear symmetry energy. In particular, we show that the predicted range for neutron star radii is robust. For use in astrophysical simulations, we provide detailed numerical tables for a representative set of equations of state consistent with these constraints. © 2013. The American Astronomical Society. All rights reserved.


Gershman A.,TU Darmstadt | Sidiropoulos N.,Technical University of Crete | Shahbazpanahi S.,University of Ontario Institute of Technology | Bengtsson M.,KTH Royal Institute of Technology | Ottersten B.,KTH Royal Institute of Technology
IEEE Signal Processing Magazine | Year: 2010

In this article, an overview of advanced convex optimization approaches to-multisensor beamforming is presented, and connections are drawn between different types of optimization-based beamformers that apply to a broad class of receive, transmit, and network beamformer design problems. It is demonstrated that convex optimization provides an indispensable set of tools for beamforming, enabling rigorous formulation and effective solution of both long-standing and emerging design problems. © 2010 IEEE.


Wallis M.G.,University of Cambridge | Moa E.,Philips | Leifland K.,Unilabs AB | Danielsson M.,KTH Royal Institute of Technology
Radiology | Year: 2012

Purpose: To compare the diagnostic accuracy of two-dimensional (2D) full-field digital mammography with that of two-view (mediolateral and craniocaudal) and single-view (mediolateral oblique) tomosynthesis in an observer study involving two institutions. Materials and Methods: Ethical committee approval was obtained. All participating women gave informed consent. Two hundred twenty women (mean age, 56.3; range, 40-80 years) with breast density of 2-4 according to American College of Radiology criteria were recruited between November 2008 and September 2009 and underwent standard treatment plus tomosynthesis with a prototype photon-counting machine. After exclusion criteria were met, this resulted in a final test set of 130 women. Ten accredited readers classified the 130 cases (40 cancers, 24 benign lesions, and 66 normal images) using 2D mammography and two-view tomosynthesis. Another 10 readers reviewed the same cases using 2D mammography but single-view tomosynthesis. The multireader, multicase receiver operating characteristic (ROC) method was applied. The significance of the observed difference in accuracy between 2D mammography and tomosynthesis was calculated. Results: For diagnostic accuracy, 2D mammography performed significantly worse than two-view tomosynthesis (average area under ROC curve [AUC] = 0.772 for 2D, AUC = 0.851 for tomosynthesis, P = .021). Significant differences were found for both masses and microcalcification (P = .037 and .049). The difference in AUC between the two modalities of -0.110 was significant (P = .03) only for the five readers with the least experience (<10 years of reading); with AUC of -0.047 for the five readers with 10 years or more experience (P = .25). No significant difference (P = .79) in reader performance was seen when 2D mammography (average AUC = 0.774) was compared with single-view tomosynthesis (average AUC = 0.775). Conclusion: Two-view tomosynthesis outperforms 2D mammography but only for readers with the least experience. The benefits were seen for both masses and microcalcification. No differences in classification accuracy was seen between and 2D mammography and single-view tomosynthesis. © RSNA, 2012.


Grant
Agency: Cordis | Branch: FP7 | Program: CP | Phase: ICT-2007.8.3 | Award Amount: 2.86M | Year: 2008

Biological olfaction outperforms chemical instrumentation in specificity, response time, detection limit, coding capacity, time stability, robustness, size, power consumption, and portability. This biological function provides outstanding performance due, to a large extent, to the unique architecture of the olfactory pathway, which combines a high degree of redundancy, an efficient combinatorial coding along with unmatched chemical information processing mechanisms. The last decade has witnessed important advances in the understanding of the computational primitives underlying the functioning of the olfactory system NEUROCHEM will develop novel computing paradigms and biomimetic artefacts for chemical sensing taking inspiration from the biological olfactory pathway. This project proposes to build computational models of its main building blocks: olfactory receptor layer, olfactory bulb, and olfactory cortex. To reduce the model complexity, models, they will go through an abstraction stage in which their processing capabilities are captured by algorithmic solutions. To demonstrate this approach, a biomimetic demonstrator will be built featuring a large-scale sensor array mimicking the olfactory receptor neuron layer. In addition, the olfactory receptor array will be interfaced to a full-scale parallel simulation model of the rat olfactory bulb and cortex. In addition, abstracted biomimetic algorithms will be implemented in an embedded system that will interface the chemical sensors. This research will provide a radically new way to process chemical signals, and it will bring performances exceeding the current state of the art provided by chemometrics.


Lin L.-L.,Shandong Normal University | Lin L.-L.,KTH Royal Institute of Technology | Wang C.-K.,Shandong Normal University | Luo Y.,KTH Royal Institute of Technology | Luo Y.,Hefei University
ACS Nano | Year: 2011

The gold-benzenedithiol-gold junction is the classic prototype of molecular electronics. However, even with the similar experimental setup, it has been difficult to reproduce the measured results because of the lack of basic information about the molecular confirmation inside the junction. We have performed systematic first principles study on the inelastic electron tunneling spectroscopy of this classic junction. By comparing the calculated spectra with four different experimental results, the most possible conformations of the molecule under different experimental conditions have been successfully determined. The relationship between the contact configuration and the resulted spectra is revealed. It demonstrates again that one should always combine the theoretical and experimental inelastic electron tunneling spectra to determine the molecular conformation in a junction. Our simulations have also suggested that in terms of the reproducibility and stability, the electromigrated nanogap technique is much better than the mechanically controllable break junction technique. © 2011 American Chemical Society.


Akrami Y.,University of Oslo | Koivisto T.S.,KTH Royal Institute of Technology | Solomon A.R.,University of Cambridge
General Relativity and Gravitation | Year: 2015

The possibility of matter coupling to two metrics at once is considered. This appears natural in the most general ghost-free, bimetric theory of gravity, where it unlocks an additional symmetry with respect to the exchange of the metrics. This double coupling, however, raises the problem of identifying the observables of the theory. It is shown that if the two metrics couple minimally to matter, then there is no physical metric to which all matter would universally couple, and that moreover such an effective metric generically does not exist even for an individual matter species. By studying point particle dynamics, a resolution is suggested in the context of Finsler geometry. © 2014, Springer Science+Business Media New York.


Hesamzadeh M.R.,KTH Royal Institute of Technology | Biggar D.R.,The Australian Competition and Consumer Commission
IEEE Transactions on Power Systems | Year: 2012

This letter proposes a new approach to the computation of extremal-Nash equilibria in a wholesale power market with transmission constraints. The approach uses linearization techniques to formulate the extremal-Nash equilibrium problem as a single-stage mixed-integer linear programming problem which can be solved with standard software. Through the introduced concept of extremal-Nash equilibria, the derived structure can efficiently locate all Nash equilibria of the game. We show that this approach offers significant performance improvements over existing approaches to computing Nash equilibria. © 2012 IEEE.


News Article | October 4, 2016
Site: www.greencarcongress.com

Electric Road Systems (ERS) are already being demonstrated on public roads in Sweden. (Earlier post.) Now, a new project in Sweden, “Research and Innovation Platform for Electric Roads”, will explore how to make the step to large-scale operation along with the supporting business ecosystem as well as technical issues such as the standardization of interfaces. Viktoria Swedish ICT is coordinating the project and us working together with the research partners Chalmers University of Technology, KTH Royal Institute of Technology, the Norwegian Institute of Transport Economics (TØI), and the Swedish National Road and Transport Research Institute (VTI); with the industry partners Fortum, Profu, Scania, Vattenfall, and Volvo Group; as well as with the deployment proposals managed by Airport City Stockholm, Region Gävleborg, and Region Kalmar. Swedish ICT is a group of research institutes engaged in information and communications technology research and development. The institutes within Swedish ICT conduct research and development in several key areas, ranging from sensors and actuators, communication networks and data analytics to visualization, interaction design and service development. Viktoria Swedish ICT is the institute focused on sustainable mobility. The various parts of electric road systems have been developed in several research projects over quite some time. Technology demonstrations are ongoing along the E16 road at Sandviken and being prepared between Arlanda Airport and Rosersberg Logistics area. Our goal is to gather and build knowledge about ERS in order to answer some of the considerable questions that remain. The project has been granted SEK19 million (US$2.2 million) in funding from the Swedish Program for Strategic Vehicle Research and Innovation (FFI) and the Swedish Transport Administration. An industry contribution of SEK8 million ($930,000) gives a total investment of SEK27 million (US$3.1 million) for a term ending in 2019. Successful introduction of ERS will require a supporting and strong innovation system. The purpose of the project is to strengthen the Swedish and Nordic research and innovation resources by building a joint knowledge base in cooperation between institutes, universities, authorities, industry, and demonstration sites. The result will include clarification of the socio-economic conditions, benefits and other effects of ERS from different actors’ perspectives. Various implementation strategies will be evaluated and success factors will be identified. The project will establish an international cooperation and provide a basis for dialogue on future standards and regulations. The project will work closely with ongoing ERS demonstrations in Sweden. The industry is participating as partners in the project and as members of an extensive reference group. We are about to secure the technical solutions needed for electric roads and electric vehicles. In order to reach a full scale implementation a series of other questions needs to be solved, e.g. on business models and electrical infrastructure. This research and innovation platform is important since it unites actors from different fields in order to find the needed solutions.


News Article | September 1, 2016
Site: globenewswire.com

TORONTO, Sept. 1, 2016 (GLOBE NEWSWIRE) -- Clothing made of citrus by-products, microbes that digest waste polyester, and an online marketplace for textile leftovers are some of the five disruptive ideas that shared the first €1 million Global Change Award grant in 2015. The challenge is designed to spur early innovations that can accelerate the shift from a linear to a circular fashion industry, with the aim of protecting the planet and our living conditions. On September 1st, the non-profit H &M Foundation opens the second Global Change Award.   Initiated by H &M Foundation in 2015, the first Global Change Award received more than 2,700 applications from 112 countries. How the €1 million grant was shared between the five winners was up to the public to decide through an online vote at www.globalchangeaward.com.   "After seeing so many fantastic innovations from around the world with the potential to transform the fashion industry, we have been very eager to open up the next round of the Global Change Award. I am also honored to welcome some new members to the expert panel like Dame Ellen MacArthur, who besides making solo sailor history in 2005, has immense knowledge about the transition to a circular economy," says Karl-Johan Persson, board member of the H &M Foundation and CEO of H &M.   Making the fashion industry circular is not just about recycling. To encourage ideas from a broader scope Global Change Award 2016 has three categories open for applications: Circular business models covering ideas on how to reuse, repair, share, digitalize or extend the life of products. Circular materials looking for ideas on new fibres, recycling techniques, leather substitutes etc and Circular processes aiming to find new methods around chemicals, water and dyeing, as well as 3D printing, demand-driven manufacturing etc.   "By bringing together innovators to develop positive solutions, the Global Change Award is a great example of the approach needed to create change, and help shift the fashion industry towards a restorative and regenerative circular economy. I am excited to join the expert panel to help find the next five innovations that can be truly game-changing," says Dame Ellen MacArthur, founder and Chair of Trustees of the Ellen MacArthur Foundation.   Other members of the expert panel to help identify the best innovations for Global Change Award 2016 include Amber Valletta, Ellis Rubinstein, Rebecca Earley, Franca Sozzani, David Roberts (new), Lewis Perkins (new), Vikram Widge (new) and Johan Kuylenstierna (new). Besides the grant, the winners also get access to a one year Innovation Accelerator organized by the H &M Foundation, in partnership with Accenture and KTH Royal Institute of Technology in Stockholm. It is designed to help ensure the innovations can stand on their own as quickly as possible, and to maximize their impact on the industry.   By catalysing green, truly ground-breaking ideas, the Global Change Award takes on one of the biggest challenges facing today's fashion industry – creating fashion for a growing population, while improving its impact on the environment. H &M Foundation initiated the challenge to speed up this process for the entire fashion industry, and neither the H &M Foundation nor the company H &M take any equity or intellectual property rights in the innovations. The aim is to influence the fashion industry as a whole.   Information about the Global Change Award, how to apply and press material are available at www.globalchangeaward.com   NOTES TO EDITORS: EXPERT PANEL KEY DATES    2016.09.01 – 2016.10.31        Apply at www.globalchangeaward.com    2016.11.01 – 2017.03.27        Expert panel screening and selection    2017.03.27 – 2017.04.02        Public online vote    2017.04.05                            Grand Award Ceremony, Stockholm, Sweden    2017.04.06 – 2018.04.06        One Year Innovation Accelerator   UPDATES ON THE GLOBAL CHANGE AWARD WINNERS 2015 The winners of the Global Change Award 2015 are currently taking part of the one year Innovation Accelerator and are making great progress. Watch winner portraits on our YouTube channel. Successfully completed trials for a scalable solvent recycling strategy needed for further upscaling. Started to develop a prototype product from cotton waste. Securing partnerships with major polyester producer and chemical companies to test technology and improve cost efficiency versus virgin materials. Expanded their R &D team with key competencies and working with major brands to assess fibre quality for large scale commercial collaborations. Developed a prototype of technology to prove the concept and value proposition for both brands and factories. Launched a pilot in China in June 2016. Invited by the local government in Nanjing to the City Expo to proceed with talks on launching a pilot project in China. The mutual aim is to find a "playground" for the algae project to start a miniature supply chain as a show case in 2017.   SOCIAL MEDIA UPDATES Facebook: Global Change Award, Twitter: @glblchangeaward, Instagram: @globalchangeaward Hashtags: #gca2016, #HMFoundation. YouTube channel: youtube.com/channel/UCnO-mFsN63PuuYzI0XgIR1A   For questions, please contact: Emily Scarlett, H &M Canada Telephone: 416.898.4807 E-mail: Emily.Scarlett@hm.com   The Global Change Award is an innovation challenge, initiated by non-profit H &M Foundation in 2015. By catalyzing early innovations that can accelerate the shift from a linear to a circular fashion industry, the aim is to protect the planet and our living conditions. An expert panel annually selects five winners that share a grant of €1 million and get access to a one-year innovation accelerator provided by the H &M Foundation, Accenture and the KTH Royal Institute of Technology in Stockholm. The global public is invited to distribute the €1 million grant between the five innovations through an online vote. The result of the vote is revealed at a grand award ceremony in Stockholm, April 2017. This is one of the world's biggest challenges for early stage innovation and the first such initiative in the fashion industry. The H &M Foundation is privately funded by the Stefan Persson family, founders and the main owners of H &M. Since 2013, the family has donated SEK 1.1 billion (USD 154 million, EUR 123 million). For further information, please visit www.globalchangeaward.com. A photo accompanying this release is available at: http://www.globenewswire.com/newsroom/prs/?pkgid=41299


News Article | April 1, 2016
Site: www.techtimes.com

The future of solar energy looks bright, as researchers were able to develop a transparent wood that can be used in solar cells and windows. Solar energy, with its multitude of benefits, does not come cheap. This is the reason why scientists from KTH Royal Institute of Technology are raving about their new discovery – transparent wood. "Transparent wood is a good material for solar cells, since it's a low-cost, readily available and renewable resource," said Wallenberg Wood Center professor Lars Berglund. He added that their study, published in Biomacromolecules, has developed a way to produce the material on a mass scale. "This becomes particularly important in covering large surfaces with solar cells," Berglund said. The optically transparent wood is a kind of wood veneer without a lignin. A lignin is a cell wall component that when chemically removed from the wood causes the wood to appear white. The chemical removal of lignin involves impregnating a white porous veneer substrate with a transparent polymer, prepolymerized methyl methacrylate (PMMA), to alter the wood's refractive index. The process enabled the researchers to come up with a material that is able to achieve light transmittance of up to 85 percent. Berglund is positive that their latest discovery would create a big impact on solar technology. He believes the material will be most suitable for creating transparent structures on a grander scale, such as solar cells and windows in buildings. Buildings with glass windows can significantly benefit from this finding as it would give them a cheaper material to use that allows light to pass through while maintaining privacy. Berglund also believes that wood, with its mechanical properties such as strength and low thermal conductivity, is the most bio-based material ideal for use in buildings. The researchers are in the process of improving the transparency of the material, maximizing the process of manufacture and experimenting on different types of wood. In 2015, researchers from University of Wisconsin-Madison developed a semiconductor made out of wood in an attempt to help curb the pressing problem of e-waste.


Grant
Agency: Cordis | Branch: FP7 | Program: CSA | Phase: INFRA-2007-1.2.3;INFRA-2007-1.2-03 | Award Amount: 3.34M | Year: 2008

The Baltic Grid Second Phase (BalticGrid-II) project is designed to increase the impact, adoption and reach, and to further improve the support of services and users of the recently created e-Infrastructure in the Baltic States. This will be achieved by an extension of the BalticGrid infrastructure to Belarus; interoperation of the gLite-based infrastructure with UNICORE and ARC based Grid resources in the region; identifying and addressing the specific needs of new scientific communities such as nano-science and engineering sciences; and by establishing new Grid services for linguistic research, Baltic Sea environmental research, data mining tools for communication modelling and bioinformatics. The e-Infrastructure, based on the successful BalticGrid project, will be fully interoperable with the pan-European e-Infrastructures established by EGEE, EGEE associated projects, and the planned EGI, with the goal of a sustained e-Infrastructure in the Baltic Region. The present BalticGrid e-Infrastructure of 26 clusters in five countries is envisaged to grow, both in capacity and capability of its computing resources. The consortium is composed of 13 leading institutions in seven countries, with 7 institutions in Estonia, Latvia and Lithuania, 2 in Belarus, 2 in Poland, and one each in Sweden and Switzerland. The overall vision is to support and stimulate scientists and services used in the Baltic region to conveniently access critical networked resources both within Europe and beyond, and thereby enable the formation of effective research collaborations.


News Article | December 4, 2015
Site: www.nanotech-now.com

Home > Press > Storing electricity in paper: An organic mixed ion-electron conductor for power electronics Abstract: Researchers at Linköping University's Laboratory of Organic Electronics, Sweden, have developed power paper -- a new material with an outstanding ability to store energy. The material consists of nanocellulose and a conductive polymer. The results have been published in Advanced Science. One sheet, 15 centimetres in diameter and a few tenths of a millimetre thick can store as much as 1 F, which is similar to the supercapacitors currently on the market. The material can be recharged hundreds of times and each charge only takes a few seconds. It's a dream product in a world where the increased use of renewable energy requires new methods for energy storage -- from summer to winter, from a windy day to a calm one, from a sunny day to one with heavy cloud cover. "Thin films that function as capacitors have existed for some time. What we have done is to produce the material in three dimensions. We can produce thick sheets," says Xavier Crispin, professor of organic electronics and co-author to the article just published in Advanced Science. Other co-authors are researchers from KTH Royal Institute of Technology, Innventia, Technical University of Denmark and the University of Kentucky. The material, power paper, looks and feels like a slightly plasticky paper and the researchers have amused themselves by using one piece to make an origami swan -- which gives an indication of its strength. The structural foundation of the material is nanocellulose, which is cellulose fibres which, using high-pressure water, are broken down into fibres as thin as 20 nm in diameter. With the cellulose fibres in a solution of water, an electrically charged polymer (PEDOT:PSS), also in a water solution, is added. The polymer then forms a thin coating around the fibres. "The covered fibres are in tangles, where the liquid in the spaces between them functions as an electrolyte," explains Jesper Edberg, doctoral student, who conducted the experiments together with Abdellah Malti, who recently completed his doctorate. The new cellulose-polymer material has set a new world record in simultaneous conductivity for ions and electrons, which explains its exceptional capacity for energy storage. It also opens the door to continued development toward even higher capacity. Unlike the batteries and capacitors currently on the market, power paper is produced from simple materials - renewable cellulose and an easily available polymer. It is light in weight, it requires no dangerous chemicals or heavy metals and it is waterproof. The Power Papers project has been financed by the Knut and Alice Wallenberg Foundation since 2012. "They leave us to our research, without demanding lengthy reports, and they trust us. We have a lot of pressure on us to deliver, but it's ok if it takes time, and we're grateful for that," says Professor Magnus Berggren, director of the Laboratory of Organic Electronics at Linköping University. The new power paper is just like regular pulp, which has to be dehydrated when making paper. The challenge is to develop an industrial-scale process for this. "Together with KTH, Acreo and Innventia we just received SEK 34 million from the Swedish Foundation for Strategic Research to continue our efforts to develop a rational production method, a paper machine for power paper," says Professor Berggren. ### Power paper -- Four world records Highest charge and capacitance in organic electronics, 1 C and 2 F (Coulomb and Farad). Highest measured current in an organic conductor, 1 A (Ampere). Highest capacity to simultaneously conduct ions and electrons. Highest transconductance in a transistor, 1 S (Siemens) Publication: An Organic Mixed Ion-Electron Conductor for Power Electronics, Abdellah Malti, Jesper Edberg, Hjalmar Granberg, Zia Ullah Khan, Jens W Andreasen, Xianjie Liu, Dan Zhao, Hao Zhang, Yulong Yao, Joseph W Brill, Isak Engquist, Mats Fahlman, Lars Wågberg, Xavier Crispin and Magnus Berggren. Advanced Science, DOI 10.1002/advs.201500305 For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


The Nomination Committee in Lindab International AB (publ) consists of Sven Hagströmer, representing Creades AB (publ), chairman, Carl Cederschiöld, representing Handelsbanken Fonder, Göran Espelund, representing Lannebo Fonder and Peter Nilsson, chairman of the Board of Lindab International AB (publ). The Nomination Committee proposes re-election of the Board members Per Bertland, Viveka Ekberg, Bent Johannesson, Peter Nilsson and Sonat Burman-Olsson. Hans Porat and Marianne Brismar have declined re-election. The Nomination Committee proposes election of John Hedberg and Anette Frumerie as new members of the Board. John Hedberg, born 1972, is President and CEO in Creades AB (publ). Before joining Creades AB (publ), John worked at NC Advisory AB, advisor to Nordic Capital Fonder, managing investments within media/telecom and industrial services. At Nordic Capital John worked i.a. with investments in Ellos, Saferoad and Quant, in which companies he served in the Board. John has previously worked at McKinsey & Co and has held various positions within Bonnier and Relacom. John has a M.Sc. in Business and Economics degree from Stockholm School of Economics. John is chairman of the Board in NOTE AB and Board member in Acne Studios och LOTS Group, a company within Scania Group. John does not hold any shares in Lindab.  As President and CEO of Creades AB (publ), he is considered as being dependent in relation to major shareholders. Anette Frumerie, born 1968, is President and CEO in Besqab AB (publ) and has previously i.a. been Business Unit President Residential Development Nordic at Skanska (publ), Business Unit Manager of Foreign Real Estate Development & Construction at JM AB (publ). She has also held several positions within the JM Group. Anette has a M.Sc. in Engineering degree from KTH Royal Institute of Technology. Anette is a Board member in Stockholms Byggmästareförening/BI Öst since 2014. Anette does not hold any shares in Lindab and she is considered as being independent in relation to the company and major shareholders. The Nomination Committee proposes re-election of Peter Nilsson as chairman of the Board. The Nomination Committee's complete proposal and reasoned statement regarding election of the Board of Directors is available at the company's website www.lindabgroup.com. Lindab develops, manufactures, markets and distributes products and system solutions for simplified construction and improved indoor climate. The products are characterised by their high quality, ease of assembly, energy efficiency, consideration towards the environment, and are delivered with high levels of service. Altogether, this increases customer value. The Group had sales of SEK 7,589 m in 2015 and is established in 32 countries with approximately 5,100 employees. The main market is non-residential construction, which accounts for 80 percent of sales, while residential accounts for 20 percent of sales. During 2015, the Nordic market accounted for 44 percent, Western Europe for 33 percent, the CEE/CIS (Central and Eastern Europe plus other former Soviet states) for 19 percent and other markets for 4 percent of total sales. The share is listed on the Nasdaq OMX Nordic Exchange, Stockholm, Mid Cap, under the ticker symbol LIAB. For more information visit www.lindabgroup.com.


The Nomination Committee in Lindab International AB (publ) consists of Sven Hagströmer, representing Creades AB (publ), chairman, Carl Cederschiöld, representing Handelsbanken Fonder, Göran Espelund, representing Lannebo Fonder and Peter Nilsson, chairman of the Board of Lindab International AB (publ). The Nomination Committee proposes re-election of the Board members Per Bertland, Viveka Ekberg, Bent Johannesson, Peter Nilsson and Sonat Burman-Olsson. Hans Porat and Marianne Brismar have declined re-election. The Nomination Committee proposes election of John Hedberg and Anette Frumerie as new members of the Board. John Hedberg, born 1972, is President and CEO in Creades AB (publ). Before joining Creades AB (publ), John worked at NC Advisory AB, advisor to Nordic Capital Fonder, managing investments within media/telecom and industrial services. At Nordic Capital John worked i.a. with investments in Ellos, Saferoad and Quant, in which companies he served in the Board. John has previously worked at McKinsey & Co and has held various positions within Bonnier and Relacom. John has a M.Sc. in Business and Economics degree from Stockholm School of Economics. John is chairman of the Board in NOTE AB and Board member in Acne Studios och LOTS Group, a company within Scania Group. John does not hold any shares in Lindab.  As President and CEO of Creades AB (publ), he is considered as being dependent in relation to major shareholders. Anette Frumerie, born 1968, is President and CEO in Besqab AB (publ) and has previously i.a. been Business Unit President Residential Development Nordic at Skanska (publ), Business Unit Manager of Foreign Real Estate Development & Construction at JM AB (publ). She has also held several positions within the JM Group. Anette has a M.Sc. in Engineering degree from KTH Royal Institute of Technology. Anette is a Board member in Stockholms Byggmästareförening/BI Öst since 2014. Anette does not hold any shares in Lindab and she is considered as being independent in relation to the company and major shareholders. The Nomination Committee proposes re-election of Peter Nilsson as chairman of the Board. The Nomination Committee's complete proposal and reasoned statement regarding election of the Board of Directors is available at the company's website www.lindabgroup.com. Lindab develops, manufactures, markets and distributes products and system solutions for simplified construction and improved indoor climate. The products are characterised by their high quality, ease of assembly, energy efficiency, consideration towards the environment, and are delivered with high levels of service. Altogether, this increases customer value. The Group had sales of SEK 7,589 m in 2015 and is established in 32 countries with approximately 5,100 employees. The main market is non-residential construction, which accounts for 80 percent of sales, while residential accounts for 20 percent of sales. During 2015, the Nordic market accounted for 44 percent, Western Europe for 33 percent, the CEE/CIS (Central and Eastern Europe plus other former Soviet states) for 19 percent and other markets for 4 percent of total sales. The share is listed on the Nasdaq OMX Nordic Exchange, Stockholm, Mid Cap, under the ticker symbol LIAB. For more information visit www.lindabgroup.com.


The Nomination Committee in Lindab International AB (publ) consists of Sven Hagströmer, representing Creades AB (publ), chairman, Carl Cederschiöld, representing Handelsbanken Fonder, Göran Espelund, representing Lannebo Fonder and Peter Nilsson, chairman of the Board of Lindab International AB (publ). The Nomination Committee proposes re-election of the Board members Per Bertland, Viveka Ekberg, Bent Johannesson, Peter Nilsson and Sonat Burman-Olsson. Hans Porat and Marianne Brismar have declined re-election. The Nomination Committee proposes election of John Hedberg and Anette Frumerie as new members of the Board. John Hedberg, born 1972, is President and CEO in Creades AB (publ). Before joining Creades AB (publ), John worked at NC Advisory AB, advisor to Nordic Capital Fonder, managing investments within media/telecom and industrial services. At Nordic Capital John worked i.a. with investments in Ellos, Saferoad and Quant, in which companies he served in the Board. John has previously worked at McKinsey & Co and has held various positions within Bonnier and Relacom. John has a M.Sc. in Business and Economics degree from Stockholm School of Economics. John is chairman of the Board in NOTE AB and Board member in Acne Studios och LOTS Group, a company within Scania Group. John does not hold any shares in Lindab.  As President and CEO of Creades AB (publ), he is considered as being dependent in relation to major shareholders. Anette Frumerie, born 1968, is President and CEO in Besqab AB (publ) and has previously i.a. been Business Unit President Residential Development Nordic at Skanska (publ), Business Unit Manager of Foreign Real Estate Development & Construction at JM AB (publ). She has also held several positions within the JM Group. Anette has a M.Sc. in Engineering degree from KTH Royal Institute of Technology. Anette is a Board member in Stockholms Byggmästareförening/BI Öst since 2014. Anette does not hold any shares in Lindab and she is considered as being independent in relation to the company and major shareholders. The Nomination Committee proposes re-election of Peter Nilsson as chairman of the Board. The Nomination Committee's complete proposal and reasoned statement regarding election of the Board of Directors is available at the company's website www.lindabgroup.com. Lindab develops, manufactures, markets and distributes products and system solutions for simplified construction and improved indoor climate. The products are characterised by their high quality, ease of assembly, energy efficiency, consideration towards the environment, and are delivered with high levels of service. Altogether, this increases customer value. The Group had sales of SEK 7,589 m in 2015 and is established in 32 countries with approximately 5,100 employees. The main market is non-residential construction, which accounts for 80 percent of sales, while residential accounts for 20 percent of sales. During 2015, the Nordic market accounted for 44 percent, Western Europe for 33 percent, the CEE/CIS (Central and Eastern Europe plus other former Soviet states) for 19 percent and other markets for 4 percent of total sales. The share is listed on the Nasdaq OMX Nordic Exchange, Stockholm, Mid Cap, under the ticker symbol LIAB. For more information visit www.lindabgroup.com.


The Nomination Committee in Lindab International AB (publ) consists of Sven Hagströmer, representing Creades AB (publ), chairman, Carl Cederschiöld, representing Handelsbanken Fonder, Göran Espelund, representing Lannebo Fonder and Peter Nilsson, chairman of the Board of Lindab International AB (publ). The Nomination Committee proposes re-election of the Board members Per Bertland, Viveka Ekberg, Bent Johannesson, Peter Nilsson and Sonat Burman-Olsson. Hans Porat and Marianne Brismar have declined re-election. The Nomination Committee proposes election of John Hedberg and Anette Frumerie as new members of the Board. John Hedberg, born 1972, is President and CEO in Creades AB (publ). Before joining Creades AB (publ), John worked at NC Advisory AB, advisor to Nordic Capital Fonder, managing investments within media/telecom and industrial services. At Nordic Capital John worked i.a. with investments in Ellos, Saferoad and Quant, in which companies he served in the Board. John has previously worked at McKinsey & Co and has held various positions within Bonnier and Relacom. John has a M.Sc. in Business and Economics degree from Stockholm School of Economics. John is chairman of the Board in NOTE AB and Board member in Acne Studios och LOTS Group, a company within Scania Group. John does not hold any shares in Lindab.  As President and CEO of Creades AB (publ), he is considered as being dependent in relation to major shareholders. Anette Frumerie, born 1968, is President and CEO in Besqab AB (publ) and has previously i.a. been Business Unit President Residential Development Nordic at Skanska (publ), Business Unit Manager of Foreign Real Estate Development & Construction at JM AB (publ). She has also held several positions within the JM Group. Anette has a M.Sc. in Engineering degree from KTH Royal Institute of Technology. Anette is a Board member in Stockholms Byggmästareförening/BI Öst since 2014. Anette does not hold any shares in Lindab and she is considered as being independent in relation to the company and major shareholders. The Nomination Committee proposes re-election of Peter Nilsson as chairman of the Board. The Nomination Committee's complete proposal and reasoned statement regarding election of the Board of Directors is available at the company's website www.lindabgroup.com. Lindab develops, manufactures, markets and distributes products and system solutions for simplified construction and improved indoor climate. The products are characterised by their high quality, ease of assembly, energy efficiency, consideration towards the environment, and are delivered with high levels of service. Altogether, this increases customer value. The Group had sales of SEK 7,589 m in 2015 and is established in 32 countries with approximately 5,100 employees. The main market is non-residential construction, which accounts for 80 percent of sales, while residential accounts for 20 percent of sales. During 2015, the Nordic market accounted for 44 percent, Western Europe for 33 percent, the CEE/CIS (Central and Eastern Europe plus other former Soviet states) for 19 percent and other markets for 4 percent of total sales. The share is listed on the Nasdaq OMX Nordic Exchange, Stockholm, Mid Cap, under the ticker symbol LIAB. For more information visit www.lindabgroup.com.


Hagfeldt A.,Uppsala University | Hagfeldt A.,KTH Royal Institute of Technology
Ambio | Year: 2012

Dye-sensitized solar cells (DSC) are based on molecular and nanometer-scale components. Record cell efficiencies of 12%, promising stability data and means of energy-efficient production methods have been accomplished. As selling points for the DSC technology the prospect of low-cost investments and fabrication are key features. DSCs offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. The basic principles of the operation of DSC, the state-of-the-art as well as the potentials for future development are described. © Royal Swedish Academy of Sciences 2012.


Murugan N.A.,KTH Royal Institute of Technology
Journal of Physical Chemistry B | Year: 2011

We have investigated the ambient temperature structure of 1-methyl-8-oxyquinolinium betaine (MOQB) in water solvent and compared to its gas-phase structure. We have employed Car-Parrinello molecular dynamics (CPMD) simulations within hybrid quantum mechanics-molecular mechanics (QM/MM) framework to study MOQB in water while CPMD technique has been used for the gas phase. We report significant solvent-induced geometrical changes in MOQB. The dipole moment of MOQB in water is 2 times larger than the gas-phase value. The average absorption spectra calculated from gas-phase configurations using Coulomb attenuated-B3LYP (CAMB3LYP) level of theory is comparable with experimental spectra reported in benzene (λmax = 590 nm), a nonpolar solvent. We have also computed the absorption spectra of MOQB in water solvent using continuum and semicontinuum solvent models. Based on this, we have calculated contributions from solvent-induced geometrical changes, hydrogen bonding, and intermolecular charge transfer to the solvatochromic shift and absorption spectra of MOQB in water. Absorption spectra calculations for MOQB in water with a semicontinuum approach for solvents using CAMB3LYP level of theory excellently reproduce the experimental spectra in water, where the theoretical λmax is 433 nm and the experimental λmax is around 440 nm. © 2011 American Chemical Society.


Conroy A.,Lancaster University | Koivisto T.,KTH Royal Institute of Technology | Mazumdar A.,Lancaster University | Teimouri A.,Lancaster University
Classical and Quantum Gravity | Year: 2015

Metric theories of gravity are studied, beginning with a general action that is quadratic in curvature and allows arbitrary inverse powers of the dAlembertian operator, resulting in infrared non-local extensions of general relativity. The field equations are derived in full generality and their consistency is checked by verifying the Bianchi identities. The weak-field limit is computed and a straightforward algorithm is presented to infer the post-Newtonian corrections directly from the action. This is then applied to various infrared gravity models including non-local dark energy and non-local massive gravity models. Generically, the Newtonian potentials are not identical and deviate from the behaviour at large distances. However, the former does not occur in a specific class of theories that does not introduce additional degrees of freedom in flat spacetime. A new non-local model within this class is proposed, defined by the exponential of the inverse dAlembertian. This model exhibits novel features, such as the weakening of the gravity in the infrared, suggesting de-gravitation of the cosmological constant. © 2015 IOP Publishing Ltd.


Blom H.,KTH Royal Institute of Technology | Widengren J.,Albanova University Center
Current Opinion in Chemical Biology | Year: 2014

High resolution Stimulated Emission Depletion (STED) microscopy has been demonstrated for fundamental studies in cells, living tissue and organisms. Today, a major trend in the STED technique development is to make the instruments simpler and more user-friendly, without compromising performance. This has become possible by new low-cost, turn-key laser technology and by implementing specifically designed phase plates and polarization elements, extending and simplifying the shaping of the laser beam profiles. These simpler and cheaper realizations of STED are now becoming more broadly available. In parallel with the continuous development of sample preparation and fluorophore reporter molecules ultimately setting the limit of the image quality, contrast and resolution, we can thus expect a significant increase in the use of STED, in science as well as for clinical and drug development purposes. © 2014.


Hao J.,KTH Royal Institute of Technology | Yan W.,KTH Royal Institute of Technology | Qiu M.,KTH Royal Institute of Technology
Applied Physics Letters | Year: 2010

A zero index metamaterial (ZIM) can be utilized to block wave (super-reflection) or conceal objects completely (cloaking). The "super-reflection" device can be realized by a Mu zero (Epsilon zero) metamaterial with a perfect electric (magnetic) conductor inclusion of arbitrary shape and size for a transverse electric (magnetic) incident wave. In contrast, a Mu zero (Epsilon zero) metamaterial with a perfect magnetic (electric) conductor inclusion for a transverse electric (magnetic) incident wave can be used to conceal objects of arbitrary shape. The underlying physics here is determined by the intrinsic properties of the ZIM. © 2010 American Institute of Physics.


Lou F.,KTH Royal Institute of Technology | Dai D.,Zhejiang University | Wosinski L.,KTH Royal Institute of Technology
Optics Letters | Year: 2012

An ultracompact polarization beam splitter (PBS) based on a dielectric-hybrid plasmonic-dielectric coupler is proposed. The device utilizes the polarization-dependent nature of hybrid plasmonic waveguides. By choosing proper waveguide parameters, a 2 × 5.1 μm2 PBS (including S-bends) with extinction ratios over 15 dB and insertion losses below 1.5 dB in the full C-band should be achievable. The effect of fabrication errors is also investigated. © 2012 Optical Society of America.


Jennings B.,Waterford Institute of Technology | Stadler R.,KTH Royal Institute of Technology
Journal of Network and Systems Management | Year: 2015

Resource management in a cloud environment is a hard problem, due to: the scale of modern data centers; the heterogeneity of resource types and their interdependencies; the variability and unpredictability of the load; as well as the range of objectives of the different actors in a cloud ecosystem. Consequently, both academia and industry began significant research efforts in this area. In this paper, we survey the recent literature, covering 250+ publications, and highlighting key results. We outline a conceptual framework for cloud resource management and use it to structure the state-of-the-art review. Based on our analysis, we identify five challenges for future investigation. These relate to: providing predictable performance for cloud-hosted applications; achieving global manageability for cloud systems; engineering scalable resource management systems; understanding economic behavior and cloud pricing; and developing solutions for the mobile cloud paradigm. © 2014, Springer Science+Business Media New York.


Janmark J.,KTH Royal Institute of Technology | Janmark J.,University of California at San Diego | Meyer D.A.,University of California at San Diego | Wong T.G.,University of California at San Diego
Physical Review Letters | Year: 2014

Grover's quantum search algorithm can be formulated as a quantum particle randomly walking on the (highly symmetric) complete graph, with one vertex marked by a nonzero potential. From an initial equal superposition, the state evolves in a two-dimensional subspace. Strongly regular graphs have a local symmetry that ensures that the state evolves in a three-dimensional subspace but most have no global symmetry. Using degenerate perturbation theory, we show that quantum random walk search on known families of strongly regular graphs, nevertheless, achieves the full quantum speed-up of Θ(N), disproving the intuition that fast quantum search requires global symmetry. © 2014 American Physical Society.


Parmryd I.,Uppsala University | Onfelt B.,KTH Royal Institute of Technology | Onfelt B.,Karolinska Institutet
FEBS Journal | Year: 2013

The surface of mammalian cells is neither smooth nor flat and cells have several times more plasma membrane than the minimum area required to accommodate their shape. We discuss the biological function of this apparent excess membrane that allows the cells to migrate and undergo shape changes and probably plays a role in signal transduction. Methods for studying membrane folding and topography - atomic force microscopy, scanning ion conductance microscopy, fluorescence polarization microscopy and linear dichroism - are described and evaluated. Membrane folding and topography is frequently ignored when interpreting microscopy data. This has resulted in several misconceptions regarding for instance colocalization, membrane organization and molecular clustering. We suggest simple ways to avoid these pitfalls and invoke Occam's razor - that simple explanations are preferable to complex ones. Topography, i.e. deviations from a smooth surface, should always be ruled out as the cause of anomalous data before other explanations are presented. Cell membranes are convoluted into submicrometer ruffles, which are impossible to resolve by most experimental techniques. Here we discuss the importance of considering such subresolution membrane organization when interpreting experimental data and give some examples of techniques where membrane topography can be probed. Finally we speculate what consequences ruffling could have for cellular processes, e. g. receptor signaling. © 2013 The Authors Journal compilation © 2013 FEBS.


Picano F.,KTH Royal Institute of Technology | Breugem W.-P.,Technical University of Delft | Mitra D.,University of Stockholm | Brandt L.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2013

Shear thickening appears as an increase of the viscosity of a dense suspension with the shear rate, sometimes sudden and violent at high volume fraction. Its origin for noncolloidal suspension with non-negligible inertial effects is still debated. Here we consider a simple shear flow and demonstrate that fluid inertia causes a strong microstructure anisotropy that results in the formation of a shadow region with no relative flux of particles. We show that shear thickening at finite inertia can be explained as an increase of the effective volume fraction when considering the dynamically excluded volume due to these shadow regions. © 2013 American Physical Society.


Guo F.,U.S. National Institute of Standards and Technology | Guo F.,University of Maryland University College | Belova L.M.,University of Maryland University College | McMichael R.D.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2013

We report ferromagnetic resonance force microscopy of confined spin-wave modes with improved, 100 nm resolution. The ferromagnetic resonance spectra in Permalloy disks (diameters ranging from 100 to 750 nm) distinguish multiple edge modes, and the images reveal distinct precession patterns. The fundamental edge mode also provides a new, localized probe of the magnetic properties of the film edge; rotation of the applied field reveals large edge property variations in nominally circular disks. As a function of disk diameter, the number of observed edge modes agrees with modeling. © 2013 American Physical Society.


Garaud J.,University of Massachusetts Amherst | Garaud J.,KTH Royal Institute of Technology | Babaev E.,University of Massachusetts Amherst | Babaev E.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2014

Arguments were recently advanced that hole-doped Ba1-xKxFe2As2 exhibits the s+is state at certain doping. Spontaneous breaking of time-reversal symmetry in the s+is state dictates that it possess domain wall excitations. Here, we discuss what are the experimentally detectable signatures of domain walls in the s+is state. We find that in this state the domain walls can have a dipolelike magnetic signature (in contrast to the uniform magnetic signature of domain walls p+ip superconductors). We propose experiments where quench-induced domain walls can be stabilized by geometric barriers and observed via their magnetic signature or their influence on the magnetization process, thereby providing an experimental tool to confirm the s+is state. © 2014 American Physical Society.


Gouteraux B.,KTH Royal Institute of Technology
Journal of High Energy Physics | Year: 2014

We show that strongly-coupled, translation-invariant holographic IR phases at finite density can be classified according to the scaling behaviour of the metric, the electric potential and the electric flux introducing four critical exponents, independently of the details of the setup. Solutions fall into two classes, depending on whether they break relativistic symmetry or not. The critical exponents determine key properties of these phases, like thermodynamic stability, the (ir)relevant deformations around them, the low-frequency scaling of the optical conductivity and the nature of the spectrum for electric perturbations. We also study the scaling behaviour of the electric flux through bulk minimal surfaces using the Hartnoll-Radicevic order parameter, and characterize the deviation from the Ryu-Takayanagi prescription in terms of the criti cal exponents. © 2014 The Author(s).


Rabkowski J.,KTH Royal Institute of Technology | Peftitsis D.,KTH Royal Institute of Technology | Nee H.-P.,KTH Royal Institute of Technology
Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC | Year: 2012

This paper describes the concept, the design, the construction, and experimental investigation of a 40 kVA inverter with Silicon Carbide Junction Field Effect Transistors. The inverter was designed to have an efficiency exceeding 99.5%. Due to the low losses free convection cooling could be used. Since no fans are used the reliability can be increased compared to solutions with fans. A very low conduction loss has been achieved by parallel connecting ten 85 mΩ normally-on JFETs in each switch position. A special gate-drive solution was applied forcing the transistors to switch very fast (approx. 20 kV/μs) resulting in very low switching losses. As the output power is almost equal to the input power a special effort was done to precisely determine the amount of semiconductor power losses via comparative thermal measurements. A detailed analysis of the measurements shows that the efficiency of the inverter is approximately 99.7% at 40 kVA. © 2012 IEEE.


Dubrova E.,KTH Royal Institute of Technology | Teslenko M.,KTH Royal Institute of Technology
IEEE/ACM Transactions on Computational Biology and Bioinformatics | Year: 2011

This paper addresses the problem of finding attractors in synchronous Boolean networks. The existing Boolean decision diagram-based algorithms have limited capacity due to the excessive memory requirements of decision diagrams. The simulation-based algorithms can be applied to larger networks, however, they are incomplete. We present an algorithm, which uses a SAT-based bounded model checking to find all attractors in a Boolean network. The efficiency of the presented algorithm is evaluated by analyzing seven networks models of real biological processes, as well as 150,000 randomly generated Boolean networks of sizes between 100 and 7,000. The results show that our approach has a potential to handle an order of magnitude larger models than currently possible. © 2006 IEEE.


Miliutenko S.,KTH Royal Institute of Technology | Bjorklund A.,KTH Royal Institute of Technology | Carlsson A.,KTH Royal Institute of Technology
Journal of Cleaner Production | Year: 2013

Asphalt waste from State roads in Sweden is usually recycled in order to preserve natural resources and reduce the burden on landfill. However, there appears to be a knowledge gap regarding the methods of asphalt recycling used by municipalities and private owners in Sweden. There is also a lack of knowledge regarding best practice from a life cycle environmental point of view. This study identified and evaluated potential ways of improving the life cycle environmental performance of asphalt recycling in Sweden. Data and information about the current situation of asphalt recycling in Sweden were collected through reviewing the literature and through interviews. It was observed that asphalt recycling practices were different for all three groups of road owners: the State, represented by the Swedish Transport Administration (STA), municipalities and industry. Life Cycle Assessment (LCA) methodology was used to identify processes within asphalt recycling and reuse that contribute a significant share of the total environmental impact (hotspots), and to compare the life cycle environmental performance of the main techniques used for asphalt recycling and reuse in Sweden: hot in-plant, hot in-place and reuse as an unbound material. The results showed that hot in-place recycling gave slightly more global warming potential (GWP) and cumulative energy demand (CED) savings than hot in-plant recycling. There were no savings of GWP and small savings of CED during asphalt reuse. It was concluded that asphalt recycling is environmentally preferable to asphalt reuse. However each method of asphalt recycling can provide different benefits, so possibilities exist for improving the environmental performance of the processes involved. These possibilities were subdivided into logistic, technical and organisational. © 2013 Elsevier Ltd. All rights reserved.


Hansson S.O.,KTH Royal Institute of Technology
Process Safety and Environmental Protection | Year: 2010

By inherent safety is meant that a hazard is eliminated rather than being managed by various add-on equipment and procedures. Practices of inherent safety have been developed in the chemical industry, and include for instance the substitution of hazardous substances by less hazardous ones. Inherently safer design strives to eliminate the possibility of major adverse events even when the probabilities of these events are small or cannot be meaningfully estimated. Considerations of security can be more easily incorporated into this approach than into most other branches of risk and safety analysis. Therefore, inherent safety has a great potential as a meeting-ground for the much-needed coordination of safety and security work. Its philosophical underpinnings are outlined, and proposals are made for more efficient promotion of its principles. © 2010 The Institution of Chemical Engineers.


Arnborg S.,KTH Royal Institute of Technology
International Journal of Approximate Reasoning | Year: 2016

In Robust Bayesian analysis one attempts to avoid the ‘Dogma of Precision’ in Bayesian analysis by entertaining a set of probability distributions instead of exactly one. The algebraic approach to plausibility calculi is inspired by Cox's and Jaynes' analyses of plausibility assessment as a logic of uncertainty. In the algebraic approach one is not so much interested in different ways to prove that precise Bayesian probability is inevitable but rather in how different sets of assumptions are reflected in the resulting plausibility calculus. It has repeatedly been pointed out that a partially ordered plausibility domain is more appropriate than a totally ordered one, but it has not yet been completely resolved exactly what such domains can look like. One such domain is the natural robust Bayesian representation, an indexed family of probabilities. We show that every plausibility calculus embeddable in a partially ordered ring is equivalent to a subring of a product of ordered fields, i.e., the robust Bayesian representation is universal under our assumptions, if extended rather than standard probability is used. We also show that this representation has at least the same expressiveness as coherent sets of desirable gambles with real valued payoffs, for a finite universe. © 2016 Elsevier Inc.


Du G.,KTH Royal Institute of Technology | Karoumi R.,KTH Royal Institute of Technology
Structure and Infrastructure Engineering | Year: 2014

Currently, the whole world is confronted with great challenges related to environmental issues. As a fundamental infrastructure in transport networks, railway bridges are responsible for numerous material and energy consumption through their life cycle, which in turn leads to significant environmental burdens. However, present management of railway bridge infrastructures is mainly focused on the technical and financial aspects, whereas the environmental assessment is rarely integrated. Life cycle assessment (LCA) is deemed as a systematic method for also assessing the environmental impact of products and systems, but its application in railway bridge infrastructures is rare. Very limited literature and research studies are available in this area. In order to incorporate the implementation of LCA into railway bridges and set new design criteria, this article performs an elaborate literature survey and presents current developments regarding the LCA implementation for railway bridges. Several critical issues are discussed and highlighted in detail. The discussion is focused on the methodology, practical operational issues and data collections. Finally, a systematic LCA framework for quantifying environmental impacts for railway bridges is introduced and interpreted as a potential guideline. © 2012 Taylor & Francis.


Pralits J.O.,University of Salerno | Brandt L.,KTH Royal Institute of Technology | Giannetti F.,University of Salerno
Journal of Fluid Mechanics | Year: 2010

The two-dimensional flow around a rotating circular cylinder is studied at Re = 100. The instability mechanisms for the first and second shedding modes are analysed. The region in the flow with a role of wavemaker in the excitation of the global instability is identified by considering the structural sensitivity of the unstable mode. This approach is compared with the analysis of the perturbation kinetic energy production, a classic approach in linear stability analysis. Multiple steady-state solutions are found at high rotation rates, explaining the quenching of the second shedding mode. Turning points in phase space are associated with the movement of the flow stagnation point. In addition, a method to examine which structural variation of the base flow has the largest impact on the instability features is proposed. This has relevant implications for the passive control of instabilities. Finally, numerical simulations of the flow are performed to verify that the structural sensitivity analysis is able to provide correct indications on where to position passive control devices, e.g. small obstacles, in order to suppress the shedding modes. Copyright © Cambridge University Press 2010.


Khatiwada D.,KTH Royal Institute of Technology | Silveira S.,KTH Royal Institute of Technology
Journal of Cleaner Production | Year: 2011

This paper evaluates life cycle greenhouse gas (GHG) balances in production and use of molasses-based ethanol (EtOH) in Nepal. The total life cycle emissions of EtOH is estimated at 432.5 kgCO2eq m-3 ethanol (i.e. 20.4 gCO2eq MJ-1). Avoided emissions are 76.6% when conventional gasoline is replaced by molasses derived ethanol. A sensitivity analysis was performed to verify the impact of variations in material and energy flows, and allocation ratios in the GHG balances. Market prices of sugar and molasses, amount of nitrogen-fertilizers used in sugarcane production, and sugarcane yield per hectare turn out to be important parameters for the GHG balances estimation. Sales of the surplus electricity derived from bagasse could reduce emissions by replacing electricity produced in diesel power plants. Scenario analysis on two wastewater processes for treatment of effluents obtained from ethanol conversion has also been carried out. If wastewater generated from ethanol conversion unit is treated in pond stabilization (PS) treatment process, GHG emissions alarmingly increase to a level of 4032 kgCO2eq m-3 ethanol. Results also show that the anaerobic digestion process (ADP) and biogas recovery without leakages can significantly avoid GHG emissions, and improve the overall emissions balance of EtOH in Nepal. At a 10% biogas leakage, life cycle emissions is 1038 kgCO 2eq m-3 ethanol which corresponds to 44% avoided emissions compared to gasoline. On the other hand, total emissions surpass the level of its counterpart (i.e. gasoline) when the leakage of biogas exceeds 23.4%. © 2011 Elsevier Ltd. All rights reserved.


Olshevsky V.,Catholic University of Leuven | Olshevsky V.,Main Astronomical Observatory of NAS | Lapenta G.,Catholic University of Leuven | Markidis S.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2013

We perform three-dimensional particle-in-cell simulations of magnetic reconnection with multiple magnetic null points. Magnetic field energy conversion into kinetic energy is about five times higher than in traditional Harris sheet configuration. More than 85% of initial magnetic field energy is transferred to particle energy during 25 reversed ion cyclofrequencies. Magnetic reconnection in the cluster of null points evolves in three phases. During the first phase, ion beams are excited, then give part of their energy back to the magnetic field in the second phase. In the third phase, magnetic reconnection occurs in many small patches around the current channels formed along the stripes of a low magnetic field. Magnetic reconnection in null points essentially presents three-dimensional features, with no two-dimensional symmetries or current sheets. © 2013 American Physical Society.


Hansson S.O.,KTH Royal Institute of Technology
Science and Engineering Ethics | Year: 2011

Research is subject to more stringent ethical requirements than most other human activities, and a procedure that is otherwise allowed may be forbidden in research. Hence, risk-taking is more restricted in scientific research than in most non-research contexts, and privacy is better protected in scientific questionnaires than in marketing surveys. Potential arguments for this difference are scrutinized. The case in its favour appears to be weak. A stronger case can be made in favour of a difference in the opposite direction: If perilous or otherwise problematic activities have to be performed it is usually better to perform them in a research context where they are properly evaluated so that guidance is obtained for the future. However, retreating from current ethical demands on research is not a desirable direction to go. Instead, research ethics can serve to inspire the introduction of more stringent ethical principles in other social sectors. © 2009 Springer Science+Business Media B.V.


Szabo Z.,KTH Royal Institute of Technology | Grenthe I.,KTH Royal Institute of Technology
Inorganic Chemistry | Year: 2010

The mechanism, rate constant, and activation parameters for the exchange between uranyl(VI) oxygen and water oxygen in tetramethyl ammonium hydroxide solution, TMA-OH, have been determined using 17O NMR magnetization transfer technique. In the concentration range investigated, the predominant complex is UO2(OH)4 2-. The experimental rate equation, rate = kex[TMA-OH]free[U(VI)]2 total indicates that the exchange takes place via a binuclear complex or transition state with the stoichiometry [(UO2(OH) 4 2-)(UO2(OH)5 3-]. The rate-determining step most likely takes place between the axial "yl" oxygens and the equatorial hydroxides. The experimental Gibbs energy of activation, δG† = 60.8 ± 2.4 kJ/mol is in good agreement with the value, δA† ≈ δG† = 52.3 ± 5.4 kJ/mol, found by Bühl and Schreckenbach in a recent Car-Parrinello molecular dynamics study, indicating that their proposed "shuttle" mechanism may be applicable also on the proposed binuclear transition state. © 2010 American Chemical Society.


Devlic A.,KTH Royal Institute of Technology
SIGCOMM'10 - Proceedings of the SIGCOMM 2010 Conference | Year: 2010

Context-aware applications need quickly access to current context information, in order to adapt their behavior before this context changes. To achieve this, the context distribution mechanism has to timely discover context sources that can provide a particular context type, then acquire and distribute context information from these sources to the applications that requested this type of information. This paper reviews the state-of-the-art context distribution mechanisms according to identified requirements, then introduces a resource list-based subscription/notification mechanism for context sharing. This SIP-based mechanism enables subscriptions to a resource list containing URIs of multiple context sources that can provide the same context type and delivery of aggregated notifications containing context updates from each of these sources. Aggregation of context is thought to be important as it reduces the network traffic between entities involved in context distribution. However, it introduces an additional delay due to waiting for context updates and their aggregation. To investigate if this aggregation actually pays off, we measured and compared the time needed by an application to receive context updates after subscribing to a particular resource list (using RLS) versus after subscribing to each of the individual context sources (using SIMPLE) for different numbers of context sources. Our results show that RLS aggregation outperforms the SIMPLE presence mechanism with 3 or more context sources, regardless of their context updates size. Database performance was identified as a major bottleneck during aggregation, hence we used in-memory tables & prepared statements, leading to up to 57% database time improvement, resulting in a reduction of the aggregation time by up to 34%. With this reduction and an increase in context size, we pushed the aggregation payoff threshold closer to 2 context sources.


Gutierrez E.,KTH Royal Institute of Technology | Magnusson M.,KTH Royal Institute of Technology
International Journal of Project Management | Year: 2014

Previous research has considered combining different decision-making approaches to be critical to achieve flexibility in Project Portfolio Management (PPM). Lacking flexibility, i.e., making decisions only by rational and formal approaches, might lead to a deficient balance between different types of ideas and projects, and this may lead to innovation opportunities being missed. However, the challenges that decision makers might face in achieving that flexibility have not been investigated thoroughly. In an interview study of three industrial companies, we explored how different decision-making approaches are combined in PPM. We found that rational and formal decision-making processes are experienced as more legitimate than informal and non-rational ones. Decision makers deal with legitimacy by certain mechanisms that allow them to bypass high accepted approaches and legitimizing decisions made by low accepted ones. We discuss how these mechanisms, while contributing to achieving flexibility, might also cause a bias in decisions and destabilization in resource allocation. © 2013 Elsevier Ltd and IPMA.


Heier J.,Dalarna University | Heier J.,KTH Royal Institute of Technology | Bales C.,Dalarna University | Martin V.,KTH Royal Institute of Technology
Renewable and Sustainable Energy Reviews | Year: 2015

Thermal Energy Storage (TES) has been a topic of research for quite some time and has proven to be a technology that can have positive effects on the energy efficiency of a building by contributing to an increased share of renewable energy and/or reduction in energy demand or peak loads for both heating and cooling. There are many TES technologies available, both commercial and emerging, and the amount of published literature on the subject is considerable. Literature discussing the combination of thermal energy storage with buildings is however lacking and it is therefore not an easy task to decide which type of TES to use in a certain building. The goal of this paper is to give a comprehensive review of a wide variety of TES technologies, with a clear focus on the combination of storage technology and building type. The results show many promising TES technologies, both for residential and commercial buildings, but also that much research still is required, especially in the fields of phase change materials and thermochemical storage. © 2014 Elsevier Ltd. All rights reserved.


Jebari K.,KTH Royal Institute of Technology
Science and Engineering Ethics | Year: 2015

A small but growing number of studies have aimed to understand, assess and reduce existential risks, or risks that threaten the continued existence of mankind. However, most attention has been focused on known and tangible risks. This paper proposes a heuristic for reducing the risk of black swan extinction events. These events are, as the name suggests, stochastic and unforeseen when they happen. Decision theory based on a fixed model of possible outcomes cannot properly deal with this kind of event. Neither can probabilistic risk analysis. This paper will argue that the approach that is referred to as engineering safety could be applied to reducing the risk from black swan extinction events. It will also propose a conceptual sketch of how such a strategy may be implemented: isolated, self-sufficient, and continuously manned underground refuges. Some characteristics of such refuges are also described, in particular the psychosocial aspects. Furthermore, it is argued that this implementation of the engineering safety strategy safety barriers would be effective and plausible and could reduce the risk of an extinction event in a wide range of possible (known and unknown) scenarios. Considering the staggering opportunity cost of an existential catastrophe, such strategies ought to be explored more vigorously. © 2014, Springer Science+Business Media Dordrecht.


Wiklund M.,KTH Royal Institute of Technology
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2012

Manipulation of biological cells by acoustic radiation forces is often motivated by its improved biocompatibility relative to alternative available methods. On the other hand, it is well known that acoustic exposure is capable of causing damage to tissue or cells, primarily due to heating or cavitation effects. Therefore, it is important to define safety guidelines for the design and operation of the utilized devices. This tutorial discusses the biocompatibility of devices designed for acoustic manipulation of mammalian cells, and different methods for quantifying the cell viability in such devices. © 2012 The Royal Society of Chemistry.


Hansson S.O.,KTH Royal Institute of Technology
Journal of Risk Research | Year: 2010

Perhaps the most fundamental divide in risk research is that between proponents of two contradictory concepts of risk. Some take risk as objectively given and determined by physical facts, whereas others see risk as a social construction that is independent of physical facts. These two views are scrutinized, and it is concluded that neither is tenable. Risk is both fact-laden and value-laden, and it contains both objective and subjective components. It is argued that both the objectivist and the subjectivist view of risk are failed attempts to rid a complex concept of much of its complexity. The real challenge is to identify the various types of factual and valuational components inherent in statements about risk and to understand how they are combined. The two oversimplifications both stand in the way of a more sophisticated analysis of risk.


Ahlroth S.,KTH Royal Institute of Technology | Finnveden G.,KTH Royal Institute of Technology
Journal of Cleaner Production | Year: 2011

In environmental systems analysis tools such as cost-benefit analysis (CBA), life-cycle assessment (LCA) and Environmental Management Systems (EMS), weighting is often used to aggregate results and compare different alternatives. There are several weighting sets available, but so far there is no set that consistently use monetary values based on actual or hypothetical market valuation of environmental degradation and depletion. In this paper, we develop a weighting set where the values are based on willingness-to-pay estimates for environmental quality, and market values for resource depletion. The weighting set is applied to three case studies and the outcome is compared with the outcomes from three other weighting sets, Ecotax02, Ecoindicator99 and EPS2000. We find that the different sets give different results in many cases. The reason for this is partly that they are based on different values and thus should give different results. However, the differences can also be explained by data gaps and different methodological choices. If weighting sets are used, it is also important to use several to reduce the risk of overlooking important impacts due to data gaps. It is also interesting to note that though Ecovalue08 and Ecotax02 give different absolute values, the results are very similar in relative terms. Thus the political and the individual willingness-to-pay estimates yield a similar ranking of the impacts. © 2011 Elsevier Ltd. All rights reserved.


Federico S.,University of Calgary | Gasser T.C.,KTH Royal Institute of Technology
Journal of the Royal Society Interface | Year: 2010

The elastic strain energy potential for nonlinear fibre-reinforced materials is customarily obtained by superposition of the potentials of the matrix and of each family of fibres. Composites with statistically oriented fibres, such as biological tissues, can be seen as being reinforced by a continuous infinity of fibre families, the orientation of which can be represented by means of a probability density function defined on the unit sphere (i.e. the solid angle). In this case, the superposition procedure gives rise to an integral form of the elastic potential such that the deformation features in the integral, which therefore cannot be calculated a priori. As a consequence, an analytical use of this potential is impossible. In this paper, we implemented this integral form of the elastic potential into a numerical procedure that evaluates the potential, the stress and the elasticity tensor at each deformation step. The numerical integration over the unit sphere is performed by means of the method of spherical designs, in which the result of the integral is approximated by a suitable sum over a discrete subset of the unit sphere. As an example of application, we modelled the collagen fibre distribution in articular cartilage, and used it in simulating displacement-controlled tests: the unconfined compression of a cylindrical sample and the contact problem in the hip joint. © 2010 The Royal Society.


Flotterod G.,KTH Royal Institute of Technology | Liu R.,University of Leeds
Journal of Intelligent Transportation Systems: Technology, Planning, and Operations | Year: 2014

This article describes the first application of a novel path flow and origin/destination (OD) matrix estimator for iterated dynamic traffic assignment (DTA) microsimulations. The presented approach, which operates on a trip-based demand representation, is derived from an agent-based DTA calibration methodology that relies on an activity-based demand model (Flötteröd, Bierlaire, & Nagel, 2011). The objective of this work is to demonstrate the transferability of the agent-based approach to the more widely used OD matrix-based demand representation. The calibration (i) operates at the same disaggregate level as the microsimulation and (ii) has drastic computational advantages over conventional OD matrix estimators in that the demand adjustments are conducted within the iterative loop of the DTA microsimulation, which results in a running time of the calibration that is in the same order of magnitude as a plain simulation. We describe an application of this methodology to the trip-based DRACULA microsimulation and present an illustrative example that clarifies its capabilities. © 2014 Copyright © Taylor and Francis Group, LLC.


Li Q.,KTH Royal Institute of Technology | Qiu M.,KTH Royal Institute of Technology
Optics Express | Year: 2010

Vertical directional coupling between a metal-insulator-metal (MIM) plasmonic waveguide and a conventional dielectric waveguide is investigated. The coupling length, extinction ratio, insertion loss and coupling efficiency of the hybrid coupler are analyzed. As an example, when the separation between the two waveguides is 250 nm, a maximum coupling efficiency of 73%, an insertion loss of -1.4 dB and an extinction ratio of 16 dB can be achieved at a coupling length of 4.5 μm at 1.55 μm wavelength. A particular feature of this hybrid coupler is that it is highly tolerant to the structural parameters of the plasmonic waveguide and the misalignment between the two waveguides. The performance of this hybrid coupler as a TM polarizer is also analyzed and a maximum extinction ratio of 44 dB and an insertion loss of-0.18 dB can be obtained. The application of this hybrid coupler includes the signal routing between plasmonic waveguides and dielectric waveguides in photonic integrated circuits and the polarization control between TE and TM modes. In addition, it provides an approach for efficiently exciting MIM plasmonic modes with conventional dielectric modes. © 2010 Optical Society of America.


Schwenk J.M.,KTH Royal Institute of Technology
Methods in molecular biology (Clifton, N.J.) | Year: 2011

Alongside the increasing availability of affinity reagents, antibody microarrays have been developed to become a powerful tool to screen for target proteins in complex samples. Besides multiplexed sandwich immunoassays, the application of directly applying labeled sample onto arrays with immobilized capture reagents offers an approach to facilitate a systematic, high-throughput analysis of body fluids such as serum or plasma. An alternative to commonly used planar arrays has become available in form of a system based on color-coded beads for the creation of antibody arrays in suspension. The assay procedure offers an uncomplicated option to screen larger numbers of serum or plasma samples with variable sets of capture reagents. In addition, the established procedure of whole sample biotinylation circumvents the purification steps, which are generally required to remove excess labeling substance. We have shown that this assay system allows detecting proteins down into lower pico-molar and higher picogram per milliliter levels with dynamic ranges over three orders of magnitude. Presently, this workflow enables the profiling of 384 clinical samples for up to 100 proteins per assay.


Branca R.M.M.,Karolinska Institutet | Orre L.M.,Karolinska Institutet | Johansson H.J.,Karolinska Institutet | Granholm V.,University of Stockholm | And 5 more authors.
Nature Methods | Year: 2014

We present a liquid chromatography-mass spectrometry (LC-MS)-based method permitting unbiased (gene prediction-independent) genome-wide discovery of protein-coding loci in higher eukaryotes. Using high-resolution isoelectric focusing (HiRIEF) at the peptide level in the 3.7-5.0 pH range and accurate peptide isoelectric point (pI) prediction, we probed the six-reading-frame translation of the human and mouse genomes and identified 98 and 52 previously undiscovered protein-coding loci, respectively. The method also enabled deep proteome coverage, identifying 13,078 human and 10,637 mouse proteins.


Vukovic O.,KTH Royal Institute of Technology | Sou K.C.,KTH Royal Institute of Technology | Dan G.,KTH Royal Institute of Technology | Sandberg H.,KTH Royal Institute of Technology
IEEE Journal on Selected Areas in Communications | Year: 2012

Critical power system applications like contingency analysis and optimal power flow calculation rely on the power system state estimator. Hence the security of the state estimator is essential for the proper operation of the power system. In the future more applications are expected to rely on it, so that its importance will increase. Based on realistic models of the communication infrastructure used to deliver measurement data from the substations to the state estimator, in this paper we investigate the vulnerability of the power system state estimator to attacks performed against the communication infrastructure. We define security metrics that quantify the importance of individual substations and the cost of attacking individual measurements. We propose approximations of these metrics, that are based on the communication network topology only, and we compare them to the exact metrics. We provide efficient algorithms to calculate the security metrics. We use the metrics to show how various network layer and application layer mitigation strategies, like single and multi-path routing and data authentication, can be used to decrease the vulnerability of the state estimator. We illustrate the efficiency of the algorithms on the IEEE 118 and 300 bus benchmark power systems. © 2012 IEEE.


Li L.,KTH Royal Institute of Technology | Ma W.,KTH Royal Institute of Technology
Transport in Porous Media | Year: 2011

An experimental study is conducted to determine the characteristics of frictional pressure drops of fluid flow in porous beds packed with non-spherical particles. The objective is to examine the applicability of the Ergun equation to flow resistance assessment for packed beds with non-spherical particles. The experiments are carried out on the POMECOFL facility at KTH. Hollow spheres and cylinders are used to pack the beds. Either water or air is chosen as the working fluid. The experimental data show that the Ergun equation is applicable to all the test beds if the effective particle diameter used in the equation is chosen as the equivalent diameter of the particles, which is the product of Sauter mean diameter and shape factor of the particles in each bed. © 2011 Springer Science+Business Media B.V.


Zhu Ryberg Y.Z.,KTH Royal Institute of Technology | Edlund U.,KTH Royal Institute of Technology | Albertsson A.-C.,KTH Royal Institute of Technology
Biomacromolecules | Year: 2011

Biomass is converted to oxygen barriers through a conceptually unconventional approach involving the preservation of the biomass native interactions and macromolecular components and enhancing the effect by created interactions with a co-component. A combined calculation/assessment model is elaborated to understand, quantify, and predict which compositions that provide an intermolecular affinity high enough to mediate the molecular packing needed to create a functioning barrier. The biomass used is a wood hydrolysate, a polysaccharide-rich but not highly refined mixture where a fair amount of the native intermolecular and intramolecular hemicelluloseslignin interactions are purposely preserved, resulting in barriers with very low oxygen permeabilities (OP) both at 50 and 80% relative humidity and considerably lower OPs than coatings based on the corresponding highly purified spruce hemicellulose, O-acetyl galactoglucomannan (AcGGM). The component interactions and mutual affinities effectively mediate an immobilization of the chain segments in a dense disordered structure, modeled through the Hansen's solubility parameter concept and quantified on the nanolength scale by positron annihilation lifetime spectrum (PALS). © 2011 American Chemical Society.


Zalejska-Jonsson A.,KTH Royal Institute of Technology
Building and Environment | Year: 2012

The aim of this paper is to investigate building performance from the occupants' perspective and to compare how the residents in low-energy multi-family buildings and conventional buildings, respectively, perceive the comfort of, and satisfaction with, indoor elements. Additionally, the study explores differences in living-in, operation and management in low-energy and conventional residential buildings. The key data was obtained by surveys sent to occupants of carefully selected comparable buildings: three low-energy and three conventional residential buildings. Responses were compared and statistical difference was tested by the Mann-Whitney test and the Kruskal-Wallis test. Findings indicate that both low-energy and conventional residential buildings have satisfied and less satisfied tenants. The occupants' satisfaction might decrease if thermal discomfort leads them to use supplementary heating; however, use of supplementary cooling does not have the same significance. Problems and concerns regarding ventilation and heating appeared in both types of buildings. Results suggest that, compared with conventional buildings, low-energy residential buildings required the same or less system adjustment, which suggests that, from a lifecycle perspective, the low-energy buildings are the better investment. Occupants' responses suggest that the " green" profile of the building has a positive impact on their environmental awareness and behaviour. This paper shows that occupants' feedback is an important part of comprehensive building performance assessment, indicating areas for improvement relevant for developers and housing managers. The presented results show that problems often identified as specific to low-energy buildings also appear in conventional buildings. © 2012 Elsevier Ltd.


Harnefors L.,ABB | Harnefors L.,KTH Royal Institute of Technology | Antonopoulos A.,KTH Royal Institute of Technology | Norrga S.,KTH Royal Institute of Technology | And 2 more authors.
IEEE Transactions on Industrial Electronics | Year: 2013

Theory for the dynamics of modular multilevel converters is developed in this paper. It is shown that the sum capacitor voltage in each arm often can be considered instead of the individual capacitor voltages, thereby significantly reducing the complexity of the system model. Two selections of the so-called insertion indices, which both compensate for the sum-capacitor-voltage ripples, are considered. The dynamic systems which respectively result from these selections are analyzed. An effective dc-bus model, which takes into account the contribution from the submodule capacitors, is obtained. Finally, explicit formulas for the stationary sum-capacitor-voltage ripples are derived. © 1982-2012 IEEE.


Liu X.-W.,Hefei University of Technology | Zhou S.,KTH Royal Institute of Technology
International Journal of Modern Physics A | Year: 2013

The Daya Bay and RENO reactor neutrino experiments have revealed that the smallest neutrino mixing angle is in fact relatively large, i.e. θ13 ≈9°. Motivated by this exciting progress, we perform a systematic study of the neutrino mass matrix Mν with one or two texture zeros, in the assumption that neutrinos are Dirac particles. Among 15 possible patterns with two texture zeros, only three turn out to be favored by current neutrino oscillation data at the 3σ level. Although all the six patterns with one texture zero are compatible with the experimental data at the 3σ level, the parameter space of each pattern is strictly constrained. Phenomenological implications of Mν on the leptonic CP violation and neutrino mass spectrum are explored, and the stability of texture zeros against the radiative corrections is also discussed. © 2013 World Scientific Publishing Company.


Dimarogonas D.V.,KTH Royal Institute of Technology | Frazzoli E.,Massachusetts Institute of Technology | Johansson K.H.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2012

Event-driven strategies for multi-agent systems are motivated by the future use of embedded microprocessors with limited resources that will gather information and actuate the individual agent controller updates. The controller updates considered here are event-driven, depending on the ratio of a certain measurement error with respect to the norm of a function of the state, and are applied to a first order agreement problem. A centralized formulation is considered first and then its distributed counterpart, in which agents require knowledge only of their neighbors' states for the controller implementation. The results are then extended to a self-triggered setup, where each agent computes its next update time at the previous one, without having to keep track of the state error that triggers the actuation between two consecutive update instants. The results are illustrated through simulation examples. © 2012 IEEE.


Zachariah D.,KTH Royal Institute of Technology | Chatterjee S.,KTH Royal Institute of Technology | Jansson M.,KTH Royal Institute of Technology
IEEE Transactions on Signal Processing | Year: 2012

For compressive sensing of dynamic sparse signals, we develop an iterative pursuit algorithm. A dynamic sparse signal process is characterized by varying sparsity patterns over time/space. For such signals, the developed algorithm is able to incorporate sequential predictions, thereby providing better compressive sensing recovery performance, but not at the cost of high complexity. Through experimental evaluations, we observe that the new algorithm exhibits a graceful degradation at deteriorating signal conditions while capable of yielding substantial performance gains as conditions improve. © -2012 IEEE.


Shi G.,KTH Royal Institute of Technology | Johansson K.H.,KTH Royal Institute of Technology
IEEE Journal on Selected Areas in Communications | Year: 2013

This paper investigates the role persistent relations play for a social network to reach a global belief agreement under discrete-time or continuous-time evolution. Each directed arc in the underlying communication graph is assumed to be associated with a time-dependent weight function, which describes the strength of the information flow from one node to another. An arc is said to be persistent if its weight function has infinite L1 or l1 norm for continuous or discrete belief evolutions, respectively. The graph that consists of all persistent arcs is called the persistent graph of the underlying network. Three necessary and sufficient conditions on agreement or ε-agreement are established. We prove that the persistent graph fully determines the convergence to a common opinion in a social network. It is shown how the convergence rate explicitly depends on the diameter of the persistent graph. For a social networking service like Facebook, our results indicate how permanent friendships need to be and what network topology they should form for the network to be an efficient platform for opinion diffusion. © 1983-2012 IEEE.


Shi G.,KTH Royal Institute of Technology | Johansson M.,KTH Royal Institute of Technology | Johansson K.H.,KTH Royal Institute of Technology
IEEE Journal on Selected Areas in Communications | Year: 2013

The dynamics of an agreement protocol interacting with a disagreement process over a common random network is considered. The model can represent the spreading of true and false information over a communication network, the propagation of faults in a large-scale control system, or the development of trust and mistrust in a society. At each time instance and with a given probability, a pair of network nodes interact. At random each of the nodes then updates its state towards the state of the other node (attraction), away from the other node (repulsion), or sticks to its current state (neglect). Agreement convergence and disagreement divergence results are obtained for various strengths of the updates for both symmetric and asymmetric update rules. Impossibility theorems show that a specific level of attraction is required for almost sure asymptotic agreement and a specific level of repulsion is required for almost sure asymptotic disagreement. A series of sufficient and/or necessary conditions are then established for agreement convergence or disagreement divergence. In particular, under symmetric updates, a critical convergence measure in the attraction and repulsion update strength is found, in the sense that the asymptotic property of the network state evolution transits from agreement convergence to disagreement divergence when this measure goes from negative to positive. The result can be interpreted as a tight bound on how much bad action needs to be injected in a dynamic network in order to consistently steer its overall behavior away from consensus. © 1983-2012 IEEE.


Ramesh C.,KTH Royal Institute of Technology | Sandberg H.,KTH Royal Institute of Technology | Johansson K.H.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2013

For a closed-loop system with a contention-based multiple access network on its sensor link, the medium access controller (MAC) may discard some packets when the traffic on the link is high. We use a local state-based scheduler to select a few critical data packets to send to the MAC. In this paper, we analyze the impact of such a scheduler on the closed-loop system in the presence of traffic, and show that there is a dual effect with state-based scheduling. In general, this makes the optimal scheduler and controller hard to find. However, by removing past controls from the scheduling criterion, we find that certainty equivalence holds. This condition is related to the classical result of Bar-Shalom and Tse, and it leads to the design of an innovations-based scheduler with a certainty equivalent controller. However, this controller is not an equivalent design for the optimal controller, in the sense of Witsenhausen. The computation of the estimate can be simplified by introducing a symmetry constraint on the scheduler. Based on these findings, we propose a dual predictor architecture for the closed-loop system, which ensures separation between scheduler, observer and controller. We present an example of this architecture, which illustrates a network-aware event-triggering mechanism. © 1963-2012 IEEE.


Brethouwer G.,KTH Royal Institute of Technology | Duguet Y.,University Paris - Sud | Schlatter P.,KTH Royal Institute of Technology
Journal of Fluid Mechanics | Year: 2012

Direct numerical simulations of subcritical rotating, stratified and magneto-hydrodynamic wall-bounded flows are performed in large computational domains, focusing on parameters where laminar and turbulent flow can stably coexist. In most cases, a regime of large-scale oblique laminar-turbulent patterns is identified at the onset of transition, as in the case of pure shear flows. The current study indicates that this oblique regime can be shifted up to large values of the Reynolds number Re by increasing the damping by the Coriolis, buoyancy or Lorentz force. We show evidence for this phenomenon in three distinct flow cases: plane Couette flow with spanwise cyclonic rotation, plane magnetohydrodynamic channel flow with a spanwise or wall-normal magnetic field, and open channel flow under stable stratification. Near-wall turbulence structures inside the turbulent patterns are invariably found to scale in terms of viscous wall units as in the fully turbulent case, while the patterns themselves remain large-scale with a trend towards shorter wavelength for increasing Re. Two distinct regimes are identified: at low Reynolds numbers the patterns extend from one wall to the other, while at large Reynolds number they are confined to the near-wall regions and the patterns on both channel sides are uncorrelated, the core of the flow being highly turbulent without any dominant large-scale structure. © 2012 Cambridge University Press.


Blennow M.,KTH Royal Institute of Technology | Schwetz T.,Max Planck Institute for Nuclear Physics
Journal of High Energy Physics | Year: 2013

The relatively large measured value of θ 13 has opened various possibilities to determine the neutrino mass ordering, among them using PINGU, the low-energy extension of the IceCube neutrino telescope, to observe matter effects in atmospheric neutrinos, or a high statistics measurement of the neutrino energy spectrum at a reactor neutrino experiment with a baseline of around 60 km, such as the Daya Bay II project. In this work we point out a synergy between these two approaches based on the fact that when data are analysed with the wrong neutrino mass ordering the best fit occurs at different values of varDelta m 312 for PINGU and Daya Bay II. Hence, the wrong mass ordering can be excluded by a mismatch of the values inferred for varDelta m 312, thanks to the excellent accuracy for varDelta m 312 of both experiments. We perform numerical studies of PINGU and Daya Bay II sensitivities and show that the synergy effect may lead to a high significance determination of the mass ordering even in situations where the individual experiments obtain only poor sensitivity. © 2013 SISSA, Trieste, Italy.


The connection-set algebra (CSA) is a novel and general formalism for the description of connectivity in neuronal network models, from small-scale to large-scale structure. The algebra provides operators to form more complex sets of connections from simpler ones and also provides parameterization of such sets. CSA is expressive enough to describe a wide range of connection patterns, including multiple types of random and/or geometrically dependent connectivity, and can serve as a concise notation for network structure in scientific writing. CSA implementations allow for scalable and efficient representation of connectivity in parallel neuronal network simulators and could even allow for avoiding explicit representation of connections in computer memory. The expressiveness of CSA makes prototyping of network structure easy. A C++ version of the algebra has been implemented and used in a large-scale neuronal network simulation (Djurfeldt et al., IBM J Res Dev 52(1/2):31-42, 2008b) and an implementation in Python has been publicly released. © Springer Science+Business Media, LLC 2012.


Wentzel H.,KTH Royal Institute of Technology
Mechanical Systems and Signal Processing | Year: 2013

Laboratory reliability testing is an important part of the vehicle development process. Test rigs are designed to reproduce accelerations or other sensor readings in a controlled environment and criteria on the duration of testing without failure are used to assure quality. An apparent difficulty of this procedure is that the damage at a point is only indirectly coupled to the accelerations measured in other points. In this paper, it is proposed to use a modal shape filter, and control the test such that the shapes that are generating stress in critical points are reproduced. A selective weighting of the mode shapes allows for accurate reproduction of the stress, and hence the damage, also in circumstances when the exact location of the excitation force cannot be reconstructed in the test. The proposed procedure is applied in two different experiments; the first aiming to reproduce the stress in a cantilever beam, and the second aiming to reproduce the stress in a truck cabin suspension. © 2013 Elsevier Ltd.


Grishin A.M.,KTH Royal Institute of Technology
Applied Physics Letters | Year: 2010

We modeled transmission and Faraday rotation characteristics of Er-doped all-garnet [Bi3 Fe5 O12 / Gd3 Ga5 O12]m photonic crystals in view of their application in C -band magneto-optical amplifiers. It is found that 48 layered 11.4 μm thick crystal at λ=1532 nm provides 45° Faraday rotation and transmission as high as 85% being pumped with 100 mW/980 nm solid state laser diode. © 2010 American Institute of Physics.


Liu Q.,KTH Royal Institute of Technology | Zhu B.,KTH Royal Institute of Technology
Applied Physics Letters | Year: 2010

Superionic conductivity becomes true based on recent developments on ceria-based nanocomposites as electrolytes with application for low temperature (300-600 °C) solid oxide fuel cells. We theoretically describe the superionic conductivity phenomena in samaria doped ceria nanocomposites. An improved effective-medium model was used to determine the ionic conductivity of the materials focusing on a core-shell structure of the as-prepared samaria doped ceria based composite particles. This work reveals the enhancement of ionic conductivity by interface proton and oxygen ion transportation in the composites, which agrees well with the experimental results. © 2010 American Institute of Physics.


Jarall S.,KTH Royal Institute of Technology
International Journal of Refrigeration | Year: 2012

Theoretical cycle data and heat transfer of HFO-1234yf were calculated and compared with those of R134a. Drop-in tests for R134a and HFO-1234yf were carried out using refrigeration unit of a hermetic rotary compressor of 550 W nominal output power and plate heat exchangers. Results of the evaporator cooling effect and heat transfer, COP, and compressor efficiency at a defined condensation temperature and similar evaporation temperatures for the two refrigerants were calculated and compared. © 2012 Elsevier Ltd and IIR. All rights reserved.


Stilbs P.,KTH Royal Institute of Technology
European Biophysics Journal | Year: 2013

Pulsed gradient spin-echo (PGSE) NMR techniques have found growing and widespread use for investigation of a variety of physicochemical phenomena in solution, because of their effect on molecular self-diffusion, and for primarily analytical purposes, for example separation of overlapping NMR bandshapes obtained from multi-component samples. A multi-component spectral separation approach previously introduced by the author (named CORE) is founded on the fact that each part of a molecule diffuses at the same rate, and thus PGSE NMR signals from each functional group will attenuate in a fully concerted fashion throughout a PGSE experiment. Numerical separation and analysis of component NMR spectra by CORE processing is therefore stabilized and steered by this prior knowledge constraint. However, even with two components and with similar self-diffusion rates, numerical instability and cross-talk between similar component self-diffusion may appear even with good experimental signal-to-noise ratio and only minor or no component spectral overlap. So-called RECORD processing was recently introduced to accompany the CORE method. In this more robust variant, spectra are divided into several sub-regions that are treated separately and combined in a later stage. The rationale for and advantages of the generic RECORD-based approach are further discussed and illustrated. A further hybrid CORE processing variant named GRECORD is suggested and briefly tested. © 2012 European Biophysical Societies' Association.


Stankovic M.S.,KTH Royal Institute of Technology | Johansson K.H.,KTH Royal Institute of Technology | Stipanovic D.M.,University of Illinois at Urbana - Champaign
IEEE Transactions on Automatic Control | Year: 2012

We consider the problem of distributed convergence to a Nash equilibrium in a noncooperative game where the players generate their actions based only on online measurements of their individual cost functions, corrupted with additive measurement noise. Exact analytical forms and/or parameters of the cost functions, as well as the current actions of the players may be unknown. Additionally, the players' actions are subject to linear dynamic constraints. We propose an algorithm based on discrete-time stochastic extremum seeking using sinusoidal perturbations and prove its almost sure convergence to a Nash equilibrium. We show how the proposed algorithm can be applied to solving coordination problems in mobile sensor networks, where motion dynamics of the players can be modeled as: 1) single integrators (velocity-actuated vehicles), 2) double integrators (force-actuated vehicles), and 3) unicycles (a kinematic model with nonholonomic constraints). Examples are given in which the cost functions are selected such that the problems of connectivity control, formation control, rendezvous and coverage control are solved in an adaptive and distributed way. The methodology is illustrated through simulations. © 2011 IEEE.


Hu L.,KTH Royal Institute of Technology | Ramstrom O.,KTH Royal Institute of Technology
Chemical Communications | Year: 2014

A dynamic azomethine ylide system was established using Sc(OTf)3 and Ag/Taniaphos as catalysts. The system was subsequently kinetically resolved in a tandem 1,3-dipolar cycloaddition process where the silver complex acted as both a reaction catalyst and an external selector, resulting in the formation of an exclusive pyrrolidine product in good yield and enantiopurity. This journal is © the Partner Organisations 2014.


Susilo Y.O.,KTH Royal Institute of Technology | Liu C.,KTH Royal Institute of Technology
Transportation | Year: 2015

Using the UK National Travel Survey from 2002 to 2006, this paper investigates the influence of households’ residential self-selectivity, parents’ perceptions on accessibilities and their travel patterns on their children daily travel mode share. In doing this, this study introduces a model structure that represents the complex interactions between the parents’ travel patterns, their perceptions on public transport services and their reported residential self-selectivity reasons and the children travel mode shares. This structure is analysed with structural equation modelling. The model estimation results show that parents’ residential self-selectivity, parents’ perceptions and satisfactions on accessibilities and their daily travel patterns significantly influence the children’s daily travel mode shares. However, the effects are not uniform across household members. This study has revealed that households’ residential self-selectivity behaviours have more correlations with the children’s non-motorised mode shares, whilst the parents’ perceptions and satisfactions on transport infrastructure and public transport service qualities have more correlations with parents’ mode shares. The results also confirm that parents’ non-motorised modes use in travelling is highly correlated with the children’s physically active travel mode shares. However, at the same time, the results also show that the effects of mothers’ car use to the children travel mode shares is more apparent than fathers’. © 2015 Springer Science+Business Media New York


Horowitz J.M.,University of Massachusetts Boston | Sandberg H.,KTH Royal Institute of Technology
New Journal of Physics | Year: 2014

In a thermodynamic process with measurement and feedback, the second law of thermodynamics is no longer valid. In its place, various second-law-like inequalities have been advanced that each incorporate a distinct additional term accounting for the information gathered through measurement. We quantitatively compare a number of these information measures using an analytically tractable model for the feedback cooling of a Brownian particle. We find that the information measures form a hierarchy that reveals a web of interconnections. To untangle their relationships, we address the origins of the information, arguing that each information measure represents the minimum thermodynamic cost to acquire that information through a separate, distinct measurement procedure. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Sattarzadeh S.S.,KTH Royal Institute of Technology | Fransson J.H.M.,KTH Royal Institute of Technology
Physics of Fluids | Year: 2014

Recent experiments have shown that miniature vortex generators (MVGs) are coveted devices to stabilize unsteady disturbances in flat plate boundary layers and to delay the onset of turbulence by modulating the base flow in the spanwise direction. The spanwise modulation is a result from the non-modal transient growth of steady and spanwise periodic streamwise vortices being generated by the MVGs. The present experimental investigation aims at studying the transient growth of non-modal disturbances induced by a spanwise periodic array of MVGs and its stabilizing effect on non-linear unsteady disturbances in the boundary layer originating from planar Tollmien-Schlichting (TS) waves. Measurements consist of cross-stream planes at different downstream locations in the boundary layer and a spatio-temporal analysis of different modes of the disturbances is carried out. In the streaky boundary layer generated by the MVGs the fundamental spanwise mode, with the same wavelength as the MVG pairs in the array, and its first harmonic, both undergo transient growth whereas the higher harmonics decay immediately downstream of the array. In the unstable region formed in the wake of the MVG blades, i.e., just downstream of the array, a wide range of spanwise modes contributes to an initial growth in the energy of unsteady disturbances. Similar behavior is observed upstream of branch II position of the neutral stability curve where the unsteady disturbances undergo a second energy growth in the unstable region. It is shown that the spatial gradients of the base flow in the wall-normal and spanwise directions are contributing to the amplification and attenuation of the TS wave disturbances, respectively, in the streaky boundary layer. © 2014 AIP Publishing LLC.


Lindbo D.,KTH Royal Institute of Technology | Tornberg A.-K.,KTH Royal Institute of Technology
Journal of Computational Physics | Year: 2011

A spectrally accurate fast method for electrostatic calculations under periodic boundary conditions is presented. We follow the established framework of FFT-based Ewald summation, but obtain a method with an important decoupling of errors: it is shown, for the proposed method, that the error due to frequency domain truncation can be separated from the approximation error added by the fast method. This has the significance that the truncation of the underlying Ewald sum prescribes the size of the grid used in the FFT-based fast method, which clearly is the minimal grid. Both errors are of exponential-squared order, and the latter can be controlled independently of the grid size. We compare numerically to the established SPME method by Essmann et al. and see that the memory required can be reduced by orders of magnitude. We also benchmark efficiency (i.e. error as a function of computing time) against the SPME method, which indicates that our method is competitive. Analytical error estimates are proven and used to select parameters with a great degree of reliability and ease. © 2011 Elsevier Inc.


Fischione C.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

Motivated by the need for fast computations in wireless sensor networks, the new F-Lipschitz optimization theory is introduced for a novel class of optimization problems. These problems are defined by simple qualifying properties specified in terms of increasing objective function and contractive constraints. It is shown that feasible F-Lipschitz problems have always a unique optimal solution that satisfies the constraints at equality. The solution is obtained quickly by asynchronous algorithms of certified convergence. F-Lipschitz optimization can be applied to both centralized and distributed optimization. Compared to traditional Lagrangian methods, which often converge linearly, the convergence time of centralized F-Lipschitz problems is at least superlinear. Distributed F-Lipschitz algorithms converge fast, as opposed to traditional Lagrangian decomposition and parallelization methods, which generally converge slowly and at the price of many message passings. In both cases, the computational complexity is much lower than traditional Lagrangian methods. Examples of application of the new optimization method are given for distributed estimation and radio power control in wireless sensor networks. The drawback of the F-Lipschitz optimization is that it might be difficult to check the qualifying properties. For more general optimization problems, it is suggested that it is convenient to have conditions ensuring that the solution satisfies the constraints at equality. © 2011 IEEE.


Ruban A.V.,KTH Royal Institute of Technology
Philosophical Magazine | Year: 2014

A single-site mean-field approach for the concentration of thermal defects in a binary intermetallic AB compound is proposed, which is a modification of previously existing Wagner-Schottky-type models. A numerical investigation of the model is done for the case of thermal defects in NiAl. © 2014 Taylor and Francis.


Hansson S.O.,KTH Royal Institute of Technology
Artificial Intelligence | Year: 2016

According to the co-occurrence test, q is (non-monotonically) inferrible from p if and only if q holds in all the reasonably plausible belief change outcomes in which p holds. A formal model is introduced that contains representations of both the co-occurrence test (for non-monotonic inference) and the Ramsey test (for conditionals). In this model, (non-nested) conditionals and non-monotonic inference satisfy the same logical principles. However, in spite of this similarity the two notions do not coincide. They should be carefully distinguished from each other. © 2016 Elsevier B.V. All rights reserved.


Delvenne J.-C.,Catholic University of Louvain | Sandberg H.,KTH Royal Institute of Technology
Physica D: Nonlinear Phenomena | Year: 2014

In this paper, we identify a class of time-varying port-Hamiltonian systems that is suitable for studying problems at the intersection of statistical mechanics and control of physical systems. Those port-Hamiltonian systems are able to modify their internal structure as well as their interconnection with the environment over time. The framework allows us to prove the First and Second Laws of thermodynamics, but also lets us apply results from optimal and stochastic control theory to physical systems. In particular, we show how to use linear control theory to optimally extract work from a single heat source over a finite time interval in the manner of Maxwell's demon. Furthermore, the optimal controller is a time-varying port-Hamiltonian system, which can be physically implemented as a variable linear capacitor and transformer. We also use the theory to design a heat engine operating between two heat sources in finite-time Carnot-like cycles of maximum power, and we compare those two heat engines. © 2013 Elsevier Inc. All rights reserved.


Bagheri S.,KTH Royal Institute of Technology
Physics of Fluids | Year: 2014

Many fluid flows, such as bluff body wakes, exhibit stable self-sustained oscillations for a wide range of parameters. Here we study the effect of weak noise on such flows. In the presence of noise, a flow with self-sustained oscillations is characterized not only by its period, but also by the quality factor. This measure gives an estimation of the number of oscillations over which periodicity is maintained. Using a recent theory [P. Gaspard, J. Stat. Phys. 106, 57 (2002)], we report on two observations. First, for weak noise the quality factor can be approximated using a linear Floquet analysis of the deterministic system; its size is inversely proportional to the inner-product between first direct and adjoint Floquet vectors. Second, the quality factor can readily be observed from the spectrum of evolution operators. This has consequences for Koopman/Dynamic mode decomposition analyses, which extract coherent structures associated with different frequencies from numerical or experimental flows. In particular, the presence of noise induces a damping on the eigenvalues, which increases quadratically with the frequency and linearly with the noise amplitude. © 2014 AIP Publishing LLC.


Bjorkman B.,KTH Royal Institute of Technology
Journal of Pragmatics | Year: 2011

This paper will report the findings of a study that has investigated spoken English as a lingua franca (ELF) usage in Swedish higher education. The material comprises digital recordings of lectures and student group-work sessions, all being naturally occurring, authentic high-stakes spoken exchange, i.e. from non-language-teaching contexts. The aim of the present paper, which constitutes a part of a larger study, has been to investigate the role pragmatic strategies play in the communicative effectiveness of English as a lingua franca. The paper will document types of pragmatic strategies as well as point to important differences between the two speech event types and the implications of these differences for English-medium education. The findings show that lecturers in ELF settings make less frequent use of pragmatic strategies than students who deploy these strategies frequently in group-work sessions. Earlier stages of the present study (Björkman, 2008a, 2008b, 2009) showed that despite frequent non-standardness in the morphosyntax level, there is little overt disturbance in student group-work, and it is highly likely that a variety of pragmatic strategies that students deploy prevents some disturbance. It is reasonable to assume that, in the absence of appropriate pragmatic strategies used often in lectures, there is an increased risk for covert disturbance. © 2010 Elsevier B.V.


Lowe D.A.,Brown University | Thorlacius L.,KTH Royal Institute of Technology | Thorlacius L.,University of Iceland
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

Within the framework of black hole complementarity, a proposal is made for an approximate interior effective field theory description. For generic correlators of local operators on generic black hole states, it agrees with the exact exterior description in a region of overlapping validity, up to corrections that are too small to be measured by typical infalling observers. © 2014 The Authors.


Qi C.,KTH Royal Institute of Technology
Reviews in Physics | Year: 2016

The advent of radioactive ion beam facilities and new detector technologies have opened up new possibilities to investigate the radioactive decays of highly unstable nuclei, in particular the proton emission, α decay and heavy cluster decays from neutron-deficient (or proton-rich) nuclei around the proton drip line. It turns out that these decay measurements can serve as a unique probe for studying the structure of the nuclei involved. On the theoretical side, the development in nuclear many-body theories and supercomputing facilities have also made it possible to simulate the nuclear clusterization and decays from a microscopic and consistent perspective. In this article we would like to review the current status of these structure and decay studies in heavy nuclei, regarding both experimental and theoretical opportunities. We then discuss in detail the recent progress in our understanding of the nuclear α formation probabilities in heavy nuclei and their indication on the underlying nuclear structure. © 2016 The Authors.


Gorton D.,KTH Royal Institute of Technology
Risk Analysis | Year: 2014

The article introduces the use of probabilistic risk assessment for modeling the incident response process of online financial services. The main contribution is the creation of incident response trees, using event tree analysis, which provides us with a visual tool and a systematic way to estimate the probability of a successful incident response process against the currently known risk landscape, making it possible to measure the balance between front-end and back-end security measures. The model is presented using an illustrative example, and is then applied to the incident response process of a Swedish bank. Access to relevant data is verified and the applicability and usability of the proposed model is verified using one year of historical data. Potential advantages and possible shortcomings are discussed, referring to both the design phase and the operational phase, and future work is presented. © 2014 Society for Risk Analysis.


Kasson P.M.,University of Virginia | Lindahl E.,KTH Royal Institute of Technology | Lindahl E.,University of Stockholm | Pande V.S.,Stanford University
Journal of the American Chemical Society | Year: 2011

Membrane interfaces are critical to many cellular functions, yet the vast array of molecular components involved make the fundamental physics of interaction difficult to define. Water has been shown to play an important role in the dynamics of small biological systems, for example when trapped in hydrophobic regions, but the molecular details of water have generally been thought dispensable when considering large membrane interfaces. Nevertheless, spectroscopic data indicate that water has distinct, ordered behavior near membrane surfaces. While coarse-grained simulations have achieved success recently in aiding understanding the dynamics of membrane assemblies, it is natural to ask, does the missing chemical nature of water play an important role? We have therefore performed atomic-resolution simulations of vesicle fusion to understand the role of chemical detail, particularly the molecular structure of water, in membrane fusion and at membrane interfaces more generally. These membrane interfaces present a form of hydrophilic confinement, yielding surprising, non-bulk-like water behavior. © 2011 American Chemical Society.


Hesaraki A.,KTH Royal Institute of Technology | Holmberg S.,KTH Royal Institute of Technology
Indoor and Built Environment | Year: 2015

The consequences on indoor air quality (IAQ) and potential of energy savings when using a variable air volume (VAV) ventilation system were studied in a newly built Swedish building. Computer simulations with IDA Indoor Climate and Energy 4 (ICE) and analytical models were used to study the IAQ and energy savings when switching the ventilation flow from 0.375-l·s-1·m-2 to 0.100-l·s-1·m-2 during unoccupancy. To investigate whether decreasing the ventilation rate to 0.1-l·s-1·m-2 during unoccupancy, based on Swedish building regulations, BBR, is acceptable and how long the reduction can last for an acceptable IAQ, four strategies with different VAV durations were proposed. This study revealed that decreasing the flow rate to 0.1-l·s-1·m-2 for more than 4-h in an unoccupied newly built building creates unacceptable IAQ in terms of volatile organic compounds concentration. Hence, if the duration of unoccupancy in the building is more than 4-h, it is recommended to increase the ventilation rate from 0.100-l·s-1·m-2 to 0.375-l·s-1·m-2 before the home is occupied. The study showed that when the investigated building was vacant for 10-h during weekdays, increasing the ventilation rate 2-h before occupants arrive home (low ventilation rate for 8-h) creates acceptable IAQ conditions. In this system, the heating requirements for ventilation air and electricity consumption for the ventilation fan were decreased by 20% and 30%, respectively. © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.


This study analysed the environmental follow-up of a public organisation from a systems thinking approach, including follow-up within different phases of operation and with different environmental management tools. The Swedish Rail Administration (SRA), a public authority responsible for Swedish rail infrastructure, was used as a case organisation. The main aim was to identify different follow-up activities during planning, construction and operation of rail infrastructure. Additional aims were to identify limiting factors for effective environmental follow-up and to provide suggestions on how SRA follow-up can better be used as an organisational learning tool. The follow-up proved to be highly influenced by Environmental Management System and was mainly used for showing compliance with legal regulations or contract requirements. Use of environmental monitoring data was limited to the specific project in which the follow-up was carried out, possibly because of the project-based structure of the organisation following rail deregulation. Theory on organisational learning was applied in the study to discuss how to improve the distribution and use of follow-up data. A more complete 'organisational memory' seems to be required for learning from experience and adapting to change. © 2011 Springer Science+Business Media, LLC.


Wohlert J.,KTH Royal Institute of Technology | Berglund L.A.,KTH Royal Institute of Technology
Journal of Chemical Theory and Computation | Year: 2011

We have constructed a coarse-grained model of crystalline cellulose to be used in molecular dynamics simulations. Using cellobiose from the recently published MARTINI coarse-grained force field for carbohydrates [Lopez, C. A. et al. J. Chem. Theory Comput. 2009, 5, 3195-3210] as a starting point, we have reparameterized the nonbonded interactions to reproduce the partitioning free energies between water and cyclohexane for a series of cellooligomers, cellobiose through cellopentaose. By extrapolating the model to longer cellooligomers, and by assigning special cellulose-cellulose nonbonded interactions, we obtain a model which gives a stable, ordered structure in water that closely resembles the crystal structure of cellulose Iβ. Furthermore, the resulting model is compatible with an existing coarse-grained force field for proteins. This is demonstrated by a simulation of the motion of the carbohydrate-binding domain of the fungal cellulase Cel7A from Trichoderma reesei on a crystalline cellulose surface. The diffusion coefficient at room temperature is calculated at Dl = 3.1×-10-11 cm 2 s-1, which is in good agreement with experimental numbers. © 2011 American Chemical Society.


Bornefalk H.,KTH Royal Institute of Technology
Medical Physics | Year: 2011

Purpose: To develop a framework for taking the spatial frequency composition of an imaging task into account when determining optimal bin weight factors for photon counting energy sensitive x-ray systems. A second purpose of the investigation is to evaluate the possible improvement compared to using pixel based weights. Methods: The Fourier based approach of imaging performance and detectability index d′ is applied to pulse height discriminating photon counting systems. The dependency of d′ on the bin weight factors is made explicit, taking into account both differences in signal and noise transfer characteristics across bins and the spatial frequency dependency of interbin correlations from reabsorbed scatter. Using a simplified model of a specific silicon detector, d′ values for a high and a low frequency imaging task are determined for optimal weights and compared to pixel based weights. Results: The method successfully identifies bins where a large point spread function degrades detection of high spatial frequency targets. The method is also successful in determining how to downweigh highly correlated bins. Quantitative predictions for the simplified silicon detector model indicate that improvements in the detectability index when applying task-based weights instead of pixel based weights are small for high frequency targets, but could be in excess of 10 for low frequency tasks where scatter-induced correlation otherwise degrade detectability. Conclusions: The proposed method makes the spatial frequency dependency of complex correlation structures between bins and their effect on the system detective quantum efficiency easier to analyze and allows optimizing bin weights for given imaging tasks. A potential increase in detectability of double digit percents in silicon detector systems operated at typical CT energies (100 kVp) merits further evaluation on a real system. The method is noted to be of higher relevance for silicon detectors than for cadmium (zink) telluride detectors. © 2011 American Association of Physicists in Medicine.


Fernaeus Y.,KTH Royal Institute of Technology | Sundstrom P.,University of Salzburg
Proceedings of the Designing Interactive Systems Conference, DIS '12 | Year: 2012

The topic of Materials has recently surfaced as a major theme within the research field of interaction design. In this paper we further discuss the need for in-depth descriptions of specific design cases, by revisiting some of our own research-through-design efforts when working with new or not yet fully explored materials for mobile interaction. We outline a series of design challenges that we see commonly arising in this domain, divided into three general themes; 1) affordances of hardware and casings, 2) experiential properties of different software solution, and 3) material properties of sensors, radio-signals, and electricity. Our main conclusion is that research in interaction design needs an extended focus on how systems are crafted from and together with properties of digital materials, and how new knowledge gained from those processes can be shared. © 2012 ACM.


Scragg J.J.,Uppsala University | Kubart T.,Uppsala University | Watjen J.T.,Uppsala University | Ericson T.,Uppsala University | And 2 more authors.
Chemistry of Materials | Year: 2013

Cu2ZnSnS4 (CZTS) is a promising material for thin film solar cells based on sustainable resources. This paper explores some consequences of the chemical instability between CZTS and the standard Mo "back contact" layer used in the solar cell. Chemical passivation of the back contact interface using titanium nitride (TiN) diffusion barriers, combined with variations in the CZTS annealing process, enables us to isolate the effects of back contact chemistry on the electrical properties of the CZTS layer that result from the synthesis, as determined by measurements on completed solar cells. It is found that instability in the back contact is responsible for large current losses in the finished solar cell, which can be distinguished from other losses that arise from instabilities in the surface of the CZTS layer during annealing. The TiN-passivated back contact is an effective barrier to sulfur atoms and therefore prevents reactions between CZTS and Mo. However, it also results in a high series resistance and thus a reduced fill factor in the solar cell. The need for high chalcogen pressure during CZTS annealing can be linked to suppression of the back contact reactions and could potentially be avoided if better inert back contacts were to be developed. © 2013 American Chemical Society.


In the present study, differential scanning calorimetry was employed to investigate the temperature induced phase separation process of poly(propylene oxide) in a pure aqueous solution and in the presence of five different potassium salts at three different concentrations. The different salts affected the phase separation temperature in accordance with the Hofmeister series with the three salts, KF, KCl and KBr, inducing a clear salting-out effect, one salt, KSCN, inducing a clear salting-in effect and one borderline salt, KI, showing a salting-in or a salting-out effect depending on the salt concentration. It was further observed that the phase separation enthalpy was almost unaffected by the presence of KF, KCl, KBr and KI, while the presence of KSCN led to a significant decrease in this quantity. This suggests that KF, KCl, KBr and KI have a very moderate influence on the PPO hydration, while KSCN appears to decrease the hydrophobic hydration of the PPO chains. The order of how the salts affect the phase separation temperature is in agreement with data for the partition coefficients of the anions between bulk water and at the air-water interface, but only partially in agreement with data related to ion hydration and water structuring effects. These observations are discussed in relation to existing models of how the different nature of the ion and polymer hydration can lead to effective attractive and repulsive ion-polymer interactions depending of the exact chemistry of the ions and the polymer. It is suggested that the previous confusion about the Hofmeister effect is due to a misleading conceptual picture of how polymer hydration is affected by the presence of ions. It is concluded that the Hofmeister effects, in the present case, can be described by a balance between the effective interactions governed by the asymmetric hydration of ions and hydrophobic polymers. This journal is © 2012 The Royal Society of Chemistry.


Zhang X.,KTH Royal Institute of Technology | Leygraf C.,KTH Royal Institute of Technology | Odnevall Wallinder I.,KTH Royal Institute of Technology
Corrosion Science | Year: 2013

Galfan coatings on steel in laboratory exposures with predeposited NaCl and cyclic wet/dry conditions exhibit nearly the same corrosion products as after 5years of marine exposure. A general scenario for corrosion product evolution on Galfan in chloride-rich atmospheres is proposed. It includes the initial formation of ZnO, ZnAl2O4 and Al2O3 and subsequent formation of Zn6Al2(OH)16CO3{dot operator}4H2O, and Zn2Al(OH)6Cl{dot operator}2H2O and/or Zn5Cl2(OH)8{dot operator}H2O. An important phase is Zn6Al2(OH)16CO3{dot operator}4H2O, which largely governs the reduced long-term zinc runoff from Galfan. A clear influence of microstructure could be observed on corrosion initiation in the slightly zinc-richer eta;-Zn phase adjacent to the β-Al phase. © 2013 Elsevier Ltd.


Edin Grimheden M.,KTH Royal Institute of Technology
Mechatronics | Year: 2013

This paper presents a study of the integration of agile methods into mechatronics design education, as performed at KTH Royal Institute of Technology. The chosen method, Scrum, and the context of the studied capstone course are presented. With the integration of Scrum into the capstone projects, an educational favorable alternative is identified, to previously used design methodologies such as more traditional stage-gate methods as the Waterfall or method or the V-model. This is due to the emphasis on early prototyping, quick feedback and incremental development. It still might not be the favorable method for use in large scale industrial development projects where formal procedures might still be preferred, but the pedagogical advantages in mechatronics education are valuable. Incremental development and rapid prototyping for example gives many opportunities for students to reflect and improve. The Scrum focus on self-organizing teams also provides a platform to practice project organization, by empowering students to take responsibility for the product development process. Among the results of this study, it is shown that it is possible and favorable to integrate Scrum in a mechatronics capstone course and that this can enhance student preparation for a future career as mechatronics designers or product developers. It is also shown that this prepares the students with a larger flexibility to handle the increased complexity in mechatronics product development and thereby enabling the project teams to deliver results faster, more reliable and with higher quality. © 2013 Elsevier Ltd. All rights reserved.


Minaev B.,KTH Royal Institute of Technology | Minaev B.,Cherkasy National University | Baryshnikov G.,Cherkasy National University | Agren H.,KTH Royal Institute of Technology
Physical Chemistry Chemical Physics | Year: 2014

Organic light-emitting device (OLED) technology has found numerous applications in the development of solid state lighting, flat panel displays and flexible screens. These applications are already commercialized in mobile phones and TV sets. White OLEDs are of especial importance for lighting; they now use multilayer combinations of organic and elementoorganic dyes which emit various colors in the red, green and blue parts of the visible spectrum. At the same time the stability of phosphorescent blue emitters is still a major challenge for OLED applications. In this review we highlight the basic principles and the main mechanisms behind phosphorescent light emission of various classes of photofunctional OLED materials, like organic polymers and oligomers, electron and hole transport molecules, elementoorganic complexes with heavy metal central ions, and clarify connections between the main features of electronic structure and the photo-physical properties of the phosphorescent OLED materials. This journal is © 2014 the Owner Societies.


Jonsson M.,KTH Royal Institute of Technology
Israel Journal of Chemistry | Year: 2014

Interfacial radiation chemistry is of key importance in nuclear technology because most materials in the vicinity of radioactive materials in nuclear power plants, reprocessing plants, and repositories for nuclear waste are exposed to ionizing radiation. Corrosion is a crucial issue for the long-term performance and safety of these installations. Nevertheless, this field is still fairly undeveloped. In this paper, the current state of the art with particular focus on reactions between aqueous radiolysis products and metal or metal oxide surfaces is discussed. The general reactivity of hydrogen peroxide and the hydroxyl radical towards oxide surfaces is discussed on the basis of recent experimental results and DFT calculations. More specific discussions on radiation-induced surface processes in a future geological repository for spent nuclear fuel are given as relevant examples. This includes radiation-induced dissolution of spent nuclear fuel in contact with groundwater, radiation-induced corrosion of copper, and radiation-induced alterations of bentonite clay. Current knowledge gaps in these areas are highlighted. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Tang S.,Gannan Normal University | Cao X.,KTH Royal Institute of Technology
Physical Chemistry Chemical Physics | Year: 2014

Hydrogenation and fluorination provide promising applications for tuning the properties of graphene-based nanomaterials. Using first-principles calculations, we investigate the electronic and magnetic properties of zigzag graphene nanoribbons (ZGNRs) supported on hydrogenated and fluorinated ZGNRs. Our results indicate that the support of zigzag graphane nanoribbon with its full width has less impact on the electronic and magnetic properties of ZGNRs, whereas the ZGNRs supported on fluorographene nanoribbons can be tuned to metal with almost degenerated ferro- and anti-ferromagnetic states due to the intrinsic polarization of substrate. The ZGNRs supported on zigzag hybrid fluorographene-graphane nanoribbons are spin-polarized half-semiconductors with distinct band gaps for spin-up and spin-down channels. Interestingly, in the absence of an external electric field, the spin-polarized band gaps of supported ZGNRs can be well modulated in the opposite direction by changing the ratio of fluorination to hydrogenation concentration in hybrid substrates. Furthermore, the ZGNRs supported on hybrid nanoribbons exhibit the half-semiconducting to half-metallic behavior transition as the interlayer spacing is gradually reduced, which is realized more easily for the hybrid support with a relatively wide fluorographene moiety compared to its narrow counterpart. Present results provide a novel way for designing substrate-supported graphene spintronic devices. This journal is © the Partner Organisations 2014.


Babaev E.,KTH Royal Institute of Technology | Babaev E.,University of Massachusetts Amherst | Carlstrom J.,KTH Royal Institute of Technology | Speight M.,University of Leeds
Physical Review Letters | Year: 2010

We show that in multiband superconductors, even an extremely small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vortices by producing long-range intervortex attraction. This type of vortex interaction results in an unusual response to low magnetic fields leading to phase separation into domains of two-component Meissner states and vortex droplets. © 2010 The American Physical Society.


Wang M.,Dalian University of Technology | Sun L.,Dalian University of Technology | Sun L.,KTH Royal Institute of Technology
ChemSusChem | Year: 2010

Photocatalytic hydrogen production by noble-metal-free molecular catalysts and related nanomaterials is discussed in this Highlight. Several recent nanomaterials, incorporating Fe- and Ni-based molecular catalysts, are highly effective for photo- and electrochemical hydrogen production, with good stabilities. © 2010 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.


Edstrom A.,KTH Royal Institute of Technology
Physica C: Superconductivity and its Applications | Year: 2013

A systematic numerical study of non-pairwise vortex interaction forces in the Ginzburg-Landau model for single-and multicomponent superconductivity is presented. The interactions are obtained by highly accurate numerical free energy minimization. In particular a three-body interaction is defined as the difference between the total interaction and sum of pairwise interactions in a system of three vortices and such interactions are studied for single and two-component type-1, type-2, and type-1.5 superconductors. In the investigated regimes, the three-body interaction is found to be short-range repulsive but long-range attractive in the type-1 case, zero in the critical κ (Bogomoln'y) case, attractive in the type-2 case and repulsive in the type-1.5 case. Some systems of four vortices are also studied and results indicate that four-body forces are of substantially less significance than the three-body interactions. © 2013 Elsevier B.V. All rights reserved.


Neretnieks I.,KTH Royal Institute of Technology
Applied Geochemistry | Year: 2014

In nuclear waste repositories concrete and bentonite are used, sometimes in contact with each other. The rate of mutual degradation of concrete and bentonite by alkaline fluids from concrete is explored using a simple model. The model considers dissolution of a soluble compound in the concrete (e.g. portlandite), which is gradually dissolved as the solubilised hydroxide and the cation(s) diffuse towards and into the bentonite in which smectite degrades by interaction with the solutes. Accounting for only the diffusion resistances in concrete and clay, the solubility of the concrete compound and the hydroxide consumption capacity of the smectite, results in a very simple analytical model. The model is tested against several published modelling results that account for reaction kinetics, reactive surface, and equilibrium data for tens to many tens of different secondary minerals. In the models that include several specified minerals often assumptions need to be made on which minerals can form. This introduces subjective assumptions. The degradation rates using the simple model are within the range of results obtained by the complex models. In the studies of the data used in these models it was found that the uncertainties in thermodynamic data are considerable and can give contradictory information on under what conditions smectite degrades. Some smectite models and thermodynamic data suggest that smectite will transform to other minerals spontaneously if there were no kinetic restrictions. © 2014 Elsevier Ltd.


Wang Y.,KTH Royal Institute of Technology | Ahlquist M.S.G.,KTH Royal Institute of Technology
Physical Chemistry Chemical Physics | Year: 2014

Two possible reactive sites (the oxo site and the Ru site) for water on a high-valent ruthenium(v) oxo complex were examined. Our results suggest that the reaction on the ruthenium (via a seven coordinate intermediate) has both a lower barrier and a product with a lower free energy than the product of addition at the oxo. © 2014 the Partner Organisations.


Stilbs P.,KTH Royal Institute of Technology
Journal of Magnetic Resonance | Year: 2010

It is demonstrated that very robust spectral component separation can be achieved through global least-squares CORE data analysis of automatically or manually selected spectral regions in complex NMR spectra in a high-resolution situation. This procedure (acronym RECORD) only takes a few seconds and quite significantly improves the effective signal/noise of the experiment as compared to individual frequency channel fitting, like in the generic HR-DOSY approach or when using basic peak height or integral fitting. Results from RECORD processing can be further used as starting value estimates for subsequent CORE analysis of spectral data with higher degree of spectral overlap. © 2010 Elsevier Inc. All rights reserved.


Li Q.,Zhejiang University | Qiu M.,Zhejiang University | Qiu M.,KTH Royal Institute of Technology
Optics Express | Year: 2013

Propagation modes and single-guiding-mode conditions of onedimensional silver nanowires based surface plasmon polariton (SPP) waveguides versus the operating wavelength (500-2000 nm) are investigated. For silver nanowires immersed in a SiO2 matrix, both shortrange SPP (SRSPP)-like modes and long-range SPP (LRSPP)-like modes can be guided. However, only the LRSPP-like modes have cutoff radii. For silver nanowires on a SiO2 substrate, the LRSPP-like modes cannot be supported due to asymmetry. While for the SRSPP-like guiding mode, it has a cutoff radius for wavelength longer than 615 nm. For wavelength shorter than 615 nm, there is no cutoff radius for the guiding modes due to the appearance of the interface modes and thus the single-guiding-mode operation is always satisfied. © 2013 Optical Society of America.


Ashwear N.,KTH Royal Institute of Technology | Eriksson A.,KTH Royal Institute of Technology
Computers and Structures | Year: 2014

This paper investigates the effect of pre-stress level on the natural frequencies of tensegrity structures. This has been established by using Euler-Bernoulli beam elements which include the effect of the axial force on the transversal stiffness. The axial-bending coupling emphasizes the non-linear dependence of the natural frequencies on the pre-stress state. Pre-stress is seen as either synchronous, considering a variable final pre-stress design or as tuning, when increasing pre-stress is followed in a planned construction sequence. It is shown that for a certain tensegrity structure, increasing the level of pre-stress may cause the natural frequencies to rise or fall. This effect is related to whether the structural behavior can be seen as compression or tension dominant. Vanishing of the lowest natural frequency of the system is shown to be related to the critical buckling load of one or several compressed components. Modes of vibration show that when the force in the compressed components approaches any type of critical buckling load, this results in lower vibration frequencies. The methods in this study can be used to plan the tuning of the considered tensegrity structure towards the design level of pre-stress, and as health monitoring tools. © 2014 Elsevier Ltd. All rights reserved.


Chen J.,KTH Royal Institute of Technology | Havtun H.,KTH Royal Institute of Technology | Palm B.,KTH Royal Institute of Technology
Applied Energy | Year: 2015

This paper presents a comprehensive investigation of an ejector refrigeration system using conventional and advanced exergy analysis. Splitting the exergy destruction within each system component into endogenous/exogenous and avoidable/unavoidable parts provides additional useful information and improves the quality of the exergy analysis. Detailed calculations of the exergy destruction parts are schematically illustrated. Conventional exergy analysis indicates that about half of the total exergy destruction is caused by the ejector and about one quarter occurs in the generator. The advanced exergy analysis reflects the strong interactions between system components. The ejector has the highest priority to be improved, followed by the condenser and then the generator. The temperature difference in the condenser has the largest influence on the exergy destruction compared to that in the generator and the evaporator, and the ejector efficiencies are also very crucial for the exergy destruction. The system performance can be largely enhanced through improvements of the ejector and the condenser as well as the generator. © 2015 Elsevier Ltd.


Lundell F.,KTH Royal Institute of Technology | Carlsson A.,University of British Columbia
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

The motion of an inertial ellipsoid in a creeping linear shear flow of a Newtonian fluid is studied numerically. This constitutes a fundamental system that is used as a basis for simulations and analysis of flows with heavy nonspherical particles. The torque on the ellipsoid is given analytically by Jeffery. This torque is coupled with the angular-momentum equation for the particle. The motion is then governed by the Stokes number St= ρe γ |2 /μ, where ρe is the density of the ellipsoid, γ is the rate of shear, | is the length of the major axis of the ellipsoid, and μ is the dynamic viscosity of the fluid. For low St (the numerical value depends on the aspect ratio of the particle), the particle motion is similar to the Jeffery orbits obtained for inertia-free particles with the addition of an orbit drift so that the particle eventually lies in the flow-gradient plane. At higher St, more drastic effects are seen. For particles oriented in the flow-gradient plane, the rotation rate increases rather abruptly to half the shear rate in a narrow range of St. For particles with other orientations, the motion goes from a kayaking motion to rotation around an oblique axis. It is suggested that, depending on aspect and density ratios, particle inertia might be sufficient to explain and model orbit drift observed previously at low Reynolds numbers. It is discussed how and when the assumption of negligible fluid inertia and strong particle inertia can be justified from a fundamental perspective for particles of different aspect ratios. © 2010 The American Physical Society.


Liu K.,KTH Royal Institute of Technology | Fridman E.,Tel Aviv University
Systems and Control Letters | Year: 2014

This paper deals with the solution bounds for time-delay systems via delay-dependent Lyapunov-Krasovskii methods. Solution bounds are widely used for systems with input saturation caused by actuator saturation or by the quantizers with saturation. We show that an additional bound for solutions is needed for the first time-interval, where t<τ(t), both in the continuous and in the discrete time. This first time-interval does not influence on the stability and the exponential decay rate analysis. The analysis of the first time-interval is important for nonlinear systems, e.g., for finding the domain of attraction. Regional stabilization of a linear (probably, uncertain) system with unknown and bounded input delay under actuator saturation is revisited, where the saturation avoidance approach is used. © 2013 Elsevier B.V. All rights reserved.


Rojas C.R.,KTH Royal Institute of Technology | Katselis D.,KTH Royal Institute of Technology | Hjalmarsson H.,KTH Royal Institute of Technology
IEEE Transactions on Signal Processing | Year: 2013

In this article, we analyze the SPICE method developed in , and establish its connections with other standard sparse estimation methods such as the Lasso and the LAD-Lasso. This result positions SPICE as a computationally efficient technique for the calculation of Lasso-type estimators. Conversely, this connection is very useful for establishing the asymptotic properties of SPICE under several problem scenarios and for suggesting suitable modifications in cases where the naive version of SPICE would not work. © 1991-2012 IEEE.


Ding L.,East China University of Science and Technology | Zhang Z.,East China University of Science and Technology | Li X.,KTH Royal Institute of Technology | Su J.,East China University of Science and Technology
Chemical Communications | Year: 2013

Two thioxanthone-based fluorescent probes exhibited prominent solvatofluorochromism, and they were further found to be useful as fluorescence indicators for the qualitative and quantitative detection of low-level water content in various solvent media. © 2013 The Royal Society of Chemistry.


Gouteraux B.,KTH Royal Institute of Technology
Journal of High Energy Physics | Year: 2014

In this work, we examine how charge is transported in a theory where momentum is relaxed by spatially dependent, massless scalars. We analyze the possible IR phases in terms of various scaling exponents and the (ir)relevance of operators in the IR effective holographic theory with a dilaton. We compute the (finite) resistivity and encounter broad families of (in)coherent metals and insulators, characterized by universal scaling behaviour. The optical conductivity at zero temperature and low frequencies exhibits power tails which can violate scaling symmetries, due to the running of the dilaton. At low temperatures, our model captures features of random-field disorder. © The Authors.


Hossenfelder S.,KTH Royal Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

It is explained why the argument by Amelino-Camelia et al. does not answer the question how to describe multiparticle states in models with a deformed Lorentz symmetry in momentum space. © 2013 American Physical Society.


Lowe D.A.,Brown University | Thorlacius L.,KTH Royal Institute of Technology | Thorlacius L.,University of Iceland
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The future apparent horizon of a black hole develops large stress energy due to quantum effects, unless the outgoing modes are in a thermal density matrix at the local Hawking temperature. It is shown for generic pure states that the deviation from thermality is so small that infalling observers will see no drama on their way to the stretched horizon, providing a derivation of black hole complementarity after the Page time. Atypical pure states, and atypical observers, may of course see surprises, but that is not surprising. © 2013 American Physical Society.


Carlmark A.,KTH Royal Institute of Technology | Malmstrom E.,KTH Royal Institute of Technology | Malkoch M.,KTH Royal Institute of Technology
Chemical Society Reviews | Year: 2013

Dendritic polymers are highly branched, globular architectures with multiple representations of functional groups. These nanoscale organic frameworks continue to fascinate researchers worldwide and are today under intensive investigation in application-driven research. A large number of potential application areas have been suggested for dendritic polymers, including theranostics, biosensors, optics, adhesives and coatings. The transition from potential to real applications is strongly dictated by their commercial accessibility, scaffolding ability as well as biocompatibility. A dendritic family that fulfills these requirements is based on the 2,2-bismethylolpropionic acid (bis-MPA) monomer. This critical review is the first of its kind to cover most of the research activities generated on aliphatic polyester dendritic architectures based on bis-MPA. It is apparent that these scaffolds will continue to be in the forefront of cutting-edge research as their structural variations are endless including dendrons, dendrimers, hyperbranched polymers, dendritic-linear hybrids and their hybridization with inorganic surfaces. © 2013 The Royal Society of Chemistry.


Vallgren A.,KTH Royal Institute of Technology | Deusebio E.,KTH Royal Institute of Technology | Lindborg E.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2011

We hypothesize that the observed wave number spectra of kinetic and potential energy in the atmosphere can be explained by assuming that there are two related cascade processes emanating from the same large-scale energy source, a downscale cascade of potential enstrophy, giving rise to the k -3 spectrum at synoptic scales and a downscale energy cascade giving rise to the k -5/3 spectrum at mesoscales. The amount of energy which is going into the downscale energy cascade is determined by the rate of system rotation, with negligible energy going downscale in the limit of very fast rotation. We present a set of simulations of a system with strong rotation and stratification, supporting these hypotheses and showing good agreement with observations. © 2011 American Physical Society.


Zhang Y.,KTH Royal Institute of Technology | Hu L.,KTH Royal Institute of Technology | Ramstrom O.,KTH Royal Institute of Technology
Chemical Communications | Year: 2013

Dynamic systems based on double parallel reactions have been generated and resolved in situ by secondary lipase-catalyzed asymmetric transformation, resulting in high chemo- and enantioselectivities. © 2013 The Royal Society of Chemistry.


Joensson H.N.,KTH Royal Institute of Technology | Andersson Svahn H.,KTH Royal Institute of Technology
Angewandte Chemie - International Edition | Year: 2012

Droplet microfluidics allows the isolation of single cells and reagents in monodisperse picoliter liquid capsules and manipulations at a throughput of thousands of droplets per second. These qualities allow many of the challenges in single-cell analysis to be overcome. Monodispersity enables quantitative control of solute concentrations, while encapsulation in droplets provides an isolated compartment for the single cell and its immediate environment. The high throughput allows the processing and analysis of the tens of thousands to millions of cells that must be analyzed to accurately describe a heterogeneous cell population so as to find rare cell types or access sufficient biological space to find hits in a directed evolution experiment. The low volumes of the droplets make very large screens economically viable. This Review gives an overview of the current state of single-cell analysis involving droplet microfluidics and offers examples where droplet microfluidics can further biological understanding. A one-off: Single-cell analysis is one of the most interesting applications for droplet microfluidics. Droplets provide robust compartments on the size scale of a single cell, and their ability to encapsulate and rapidly manipulate cells along with their immediate environment in monodisperse compartments allows the possibility of automation. This Review focuses on single-cell analyses and applications in drug screening and genetic and enzyme analysis. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Carlmark A.,KTH Royal Institute of Technology | Larsson E.,KTH Royal Institute of Technology | Malmstrom E.,KTH Royal Institute of Technology
European Polymer Journal | Year: 2012

In this review, homogeneous and heterogeneous grafting from cellulose and cellulose derivatives by ring-opening polymerisation (ROP) are reported. Cellulose is biorenewable and biodegradable as well as a stiff material with a relatively low specific weight, foreseen to be an excellent replacement for synthetic materials. By utilising ROP of monomers such as -caprolactone or l-lactide from cellulose, composite materials with new and/or improved properties can be obtained. Grafting of solid cellulose substrates, such as cotton, microfibrillated cellulose (MFC) or cellulose nanocrystals, renders cellulose that can easily be dispersed into polymer matrices and may be used as reinforcing elements to improve mechanical and/or barrier properties of biocomposites. A surface grafted polymer can also tailor the interfacial properties between a matrix and the fibrillar structure of cellulose. When derivatives of cellulose are grafted with polymers in homogenous media, amphiphilic materials with interesting properties can be achieved, anticipated to be utilised for applications such as encapsulation and release. © 2012 Elsevier Ltd. All rights reserved.


Andreasson M.,KTH Royal Institute of Technology | Dimarogonas D.V.,KTH Royal Institute of Technology | Sandberg H.,KTH Royal Institute of Technology | Johansson K.H.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2014

This paper analyzes distributed control protocols for first- and second-order networked dynamical systems. We propose a class of nonlinear consensus controllers where the input of each agent can be written as a product of a nonlinear gain, and a sum of nonlinear interaction functions. By using integral Lyapunov functions, we prove the stability of the proposed control protocols, and explicitly characterize the equilibrium set. We also propose a distributed proportional-integral (PI) controller for networked dynamical systems. The PI controllers successfully attenuate constant disturbances in the network. We prove that agents with single-integrator dynamics are stable for any integral gain, and give an explicit tight upper bound on the integral gain for when the system is stable for agents with double-integrator dynamics. Throughout the paper we highlight some possible applications of the proposed controllers by realistic simulations of autonomous satellites, power systems and building temperature control. © 2014 IEEE.


Vukovic O.,KTH Royal Institute of Technology | Dan G.,KTH Royal Institute of Technology
IEEE Journal on Selected Areas in Communications | Year: 2014

State estimation (SE) plays an essential role in the monitoring and supervision of power systems. In today's power systems, SE is typically done in a centralized or in a hierarchical way, but as power systems will be increasingly interconnected in the future smart grid, distributed SE will become an important alternative to centralized and hierarchical solutions. As the future smart grid may rely on distributed SE, it is essential to understand the potential vulnerabilities that distributed SE may have. In this paper, we show that an attacker that compromises the communication infrastructure of a single control center in an interconnected power system can successfully perform a denial-of-service attack against state-of-the-art distributed SE, and consequently, it can blind the system operators of every region. As a solution to mitigate such a denial-of-service attack, we propose a fully distributed algorithm for attack detection. Furthermore, we propose a fully distributed algorithm that identifies the most likely attack location based on the individual regions' beliefs about the attack location, isolates the identified region, and then reruns the distributed SE. We validate the proposed algorithms on the IEEE 118 bus benchmark power system. © 2014 IEEE.


Bjornson E.,Linköping University | Bengtsson M.,KTH Royal Institute of Technology | Ottersten B.,KTH Royal Institute of Technology
IEEE Signal Processing Magazine | Year: 2014

Transmit beamforming is a versatile technique for signal transmission from an array of antennas to one or multiple users [1]. In wireless communications, the goal is to increase the signal power at the intended user and reduce interference to nonintended users. A high signal power is achieved by transmitting the same data signal from all antennas but with different amplitudes and phases, such that the signal components add coherently at the user. Low interference is accomplished by making the signal components add destructively at nonintended users. This corresponds mathematically to designing beamforming vectors (that describe the amplitudes and phases) to have large inner products with the vectors describing the intended channels and small inner products with nonintended user channels. © 2014 IEEE.


Vadiee A.,KTH Royal Institute of Technology | Martin V.,KTH Royal Institute of Technology
Renewable and Sustainable Energy Reviews | Year: 2012

The commercial greenhouse has the highest demand for energy as compared to all other agricultural industry sectors. Here, energy management is important from a broad sustainability perspective. This paper presents the state-of-the-art regarding one energy management concept; the closed greenhouse integrated with thermal energy storage (TES) technology. This concept is an innovation for sustainable energy management since it is designed to maximize the utilization of solar energy through seasonal storage. In a fully closed greenhouse, there is no ventilation which means that excess sensible and latent heat must be removed. Then, this heat can be stored using seasonal and/or daily TES technology, and used later in order to satisfy the heating demand of the greenhouse. This assessment shows that closed greenhouse can, in addition to satisfying its own heating demand, also supply the demand for neighboring buildings. Several energy potential studies show that summer excess heat of almost three times the annual heating demand of the greenhouse. However, many studies propose the use of some auxiliary system for peak load. Also, the assessment clearly point out that a combination of seasonal and short-term TES must be further explored to make use of the full potential. Although higher amount of solar energy can be harvested in a fully closed greenhouse, in reality a semi-closed greenhouse concept may be more applicable. There, a large part of the available excess heat will be stored, but the benefits of an integrated forced-ventilation system are introduced in order to use fresh air as a rapid response for primarily humidity control. The main conclusion from this review is that aspects like energy efficiency, environmental benefits and economics must be further examined since this is seldom presented in the literature. Also, a variety of energy management scenarios may be employed depending on the most prioritized aspect. © 2012 Elsevier Ltd. All rights reserved.


Mainali B.,KTH Royal Institute of Technology | Silveira S.,KTH Royal Institute of Technology
Renewable Energy | Year: 2013

The discussion on electrification pathways tends to dangle between the merits of centralized on-grid versus decentralized off-grid electrification, and most of the time, both routes are promoted in parallel. However, the basis for choosing pathways has neither been very clear nor rational. This study compares three pathways for rural electrification considering (i) off-grid renewable energy (RE) technologies for individual households (ii) mini grids (with micro hydro and diesel generators) and (iii) grid extension. Different technological pathways are analyzed considering various technical and socio-economic parameters in two country cases: Nepal and Afghanistan. Levelized cost of electricity (LCOE) is taken as the main basis for comparison of the various options, in which both environmental externalities and life cycle costs are considered. The analysis shows that the micro hydro based mini grid technology is the most competitive alternative for electrifying isolated and remote rural areas in both countries. Individual household technology should be promoted only in places with scattered households where there is no possibility of mini grid solution. The choice of technology and the pathway adopted in Nepal seems functional, though some flaws within the pathways need to be addressed. In Afghanistan, the technological pathways for rural electrification are not well-defined and the country lacks a clear cut national policy framework for rural electrification. Here, micro hydro based mini grid would be a more sustainable proposition rather than diesel generators as promoted in the transitional phase. Afghanistan can benefit from lessons learnt in Nepal not least in the formation of markets for renewable technologies. © 2013 Elsevier Ltd.


Lourdudoss S.,KTH Royal Institute of Technology
Current Opinion in Solid State and Materials Science | Year: 2012

This article reviews the major achievements in recent years on heteroepitaxy and selective area heteroepitaxy that are relevant to silicon photonics. Material aspects are given due importance without trying to cover all kinds of devices. Under heteroepitaxy several systems based on GaAs, InP and GaSb and their related materials and dilute III-nitrides all on Si substrates are covered and assessed. Quantum dot and quantum well lasers are taken as device examples. The potential of the emerging SnGeSi/Si system is highlighted. Under selective area heteroepitaxy, growth of InP from SiO 2 trenches in Si and epitaxial lateral overgrowth of InP on silicon are exemplified as the potential routes for monolithic integration on silicon. The expected trends and anticipated advances are indicated. © 2012 Elsevier Ltd. All rights reserved.


Moberg C.,KTH Royal Institute of Technology
Israel Journal of Chemistry | Year: 2012

Chiral ligands and metal complexes with rotational (C n, D n) symmetry often have beneficial properties in asymmetric catalysis. The enhanced enantioselectivity frequently observed is a result of a reduction of competing reaction routes. This may be due to rotational symmetry in the catalyst, leading to a limited number of different catalyst-substrate interactions, or to formation of a limited number of catalytic species as a result of rotational symmetry in the ligand. The effect of symmetry is usually difficult to evaluate, since a change in symmetry properties necessarily is accompanied by structural modifications. In each situation the number of intermediate complexes, their electronic and steric properties, and their energy need to be analyzed. Although other factors may be more important than symmetry for achieving high enantioselectivity, a vast number of C 2- and to some extent C 3-symmetric ligands have been found to have excellent properties in asymmetric catalysis, providing products with high enantiomeric purity. Besides the benefit of symmetry in the ligand and catalyst, the symmetry of the substrate may be important since a gain in enantioselectivity can result from simultaneous asymmetric transformations of homotopic functional groups. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wang M.,Dalian University of Technology | Chen L.,Dalian University of Technology | Sun L.,Dalian University of Technology | Sun L.,KTH Royal Institute of Technology
Energy and Environmental Science | Year: 2012

This perspective article reviews the recent important progress in electrocatalytic hydrogen production catalyzed by earth-abundant metal complexes. The catalysts are divided into two categories depending on the media used in the hydrogen-evolving reactions, with an emphasis on the types of acids employed. The catalysts used in the first category, which work in organic solutions, include nickel and cobalt complexes with base-containing diphosphine ligands, cobaloximes, cobalt tetrapyridine complexs, and [NiFe]- and [FeFe]-hydrogenase mimics. Molybdenum and cobalt pentapyridine complexes, as well as the cobalt bis(iminopyridine) complex reported very recently, are the most important examples of catalysts used in the second category, which work in aqueous solutions. The advantages and disadvantages of the different types of catalysts are discussed and the hydrogen-evolving mechanisms for the well-studied catalysts are illustrated. In addition, several molecular catalyst-modified electrodes for hydrogen production are described. © 2012 The Royal Society of Chemistry.


Gasser T.C.,KTH Royal Institute of Technology | Forsell C.,KTH Royal Institute of Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2011

The present study developed a conceptual framework for finite strain viscoelasticity thought to be suitable to capture the salient features of a class of passive soft biological tissues like the myocardium. A superposition of a Maxwell Body and an Elastic Body defines the viscoelastic continuum, and its deformation is related to two independent reference configurations. The reference configuration of the Maxwell Body moves in space as it is described (apart from rigid body rotation) by a rate equation in strain space, and stores the history of the deformation. At thermodynamic equilibrium the reference configuration of the Maxwell Body coincides with the current configuration of the continuum. The Helmholtz free energy is expressed as a function of two independent strain variables and entirely renders the constitution of the viscoelastic body. Although this view is to some extent different from reported viscoelastic concepts for finite strains, its linearization around the thermodynamic equilibrium coincides with earlier suggested viscoelastic models. The linearized viscoelastic model has been implemented for a particular anisotropic constitutive model for the passive myocardium. Non-negative dissipation of the model is guaranteed. Material parameters were estimated from in vitro testing of porcine myocardium and the response due to pushing a rigid punch into the myocardium was studied. Results between anisotropic and isotropic descriptions of the myocardium differed significantly, which justified the implementation of an anisotropic model for the myocardium. © 2011 Elsevier B.V.


Sung K.W.,KTH Royal Institute of Technology | Kim S.-L.,Yonsei University | Zander J.,KTH Royal Institute of Technology
IEEE Transactions on Wireless Communications | Year: 2010

In this paper we investigate the opportunistic spectrum access in temporal domain where a secondary user shares a radio channel with a primary user during the OFF period of the primary user. We consider practical ON/OFF traffic models whose bursty natures are not properly described by a Markovian assumption. An optimal strategy to determine the transmission power of the secondary user is proposed, which can be adapted to any source traffic model of the primary user. This strategy will maximize the spectrum utilization of the secondary user while keeping interference violations to the primary user below a threshold. Numerical results show that the transmission power of the secondary user depends on the probability distribution of the primary traffic as well as the elapsed time of the OFF period. © 2006 IEEE.


Siebentritt S.,University of Luxembourg | Igalson M.,Warsaw University of Technology | Persson C.,KTH Royal Institute of Technology | Lany S.,National Renewable Energy Laboratory
Progress in Photovoltaics: Research and Applications | Year: 2010

We summarize the progress made recently in understanding the electronic structure of chalcopyrites. New insights into the dispersion of valence and conduction band allow conclusions on the effective masses of charge carriers and their orientation dependence, which influences the transport in solar cell absorbers of different orientation. Native point defects are responsible for the doping and thus the band bending in solar cells. Results of optoelectronic defect spectroscopy are reviewed. Native defects are also the source for a number of metastabilities, which strongly affect the efficiency of solar cells. Recent theoretical findings relate these effects to the Se vacancy and the InCu antisite defect. Experimentally determined activation energies support these models. Absorbers in chalcopyrite solar cells are polycrystalline, which is only possible because of the benign character of the grain boundaries. This can be related to an unusual electronic structure of the GB. Copyright © 2010 John Wiley & Sons, Ltd.


Tolias P.,KTH Royal Institute of Technology
Plasma Physics and Controlled Fusion | Year: 2014

The description of secondary electron emission, as presented by plasma-material interaction fusion compendia, is demonstrated to be outdated both in its theoretical and experimental aspects. As a consequence, the recommended treatment leads to a strong overestimation of the secondary electron emission yields for tokamak relevant materials. Reliable experimental data-sets, in fusion energy ranges, are identified after a detailed review of a recently updated electron-solid interaction database and previously published experimental results. A novel semi-empirical approach is proposed for the description of the secondary electron emission yield. Application of the approach for a large number of solids reveals an unprecedented agreement with experimental data. The present results can serve as a reliable input for future quantitative investigations of the effect of secondary electron emission on various aspects of scrape-off-layer physics. © 2014 IOP Publishing Ltd.


Burgess J.M.,The Oskar Klein Center | Burgess J.M.,KTH Royal Institute of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2014

The understanding of the prompt γ-ray spectra of gamma-ray bursts (GRBs) is of great importance to correctly interpret the physical mechanisms that produce the underlying event as well as the structure of the relativistic jet from which the emission emanates. Time-resolved analysis of these spectra is the main method of extracting information from the data. In this work, several techniques for temporal binning of GRB spectra are examined to understand the systematics associated with each with the goal of finding the best method(s) to bin light curves for analysis. The following binning methods are examined: constant cadence (CC), Bayesian blocks (BBs), signal-to-noise (S/N) and Knuth bins (KB). I find that both the KB and BB methods reconstruct the intrinsic spectral evolution accurately while the S/N method fails in most cases. The CC method is accurate when the cadence is not too coarse but does not necessarily bin the data based on the true source variability. Additionally, the integrated pulse properties are investigated and compared to the time-resolved properties. If intrinsic spectral evolution is present, then the integrated properties are not useful in identifying physical and cosmological properties of GRBs without knowing the physical emission mechanism and its evolution. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.


Lindborg P.,Nanyang Technological University | Lindborg P.,KTH Royal Institute of Technology
Applied Acoustics | Year: 2015

Sound is a multi-faceted phenomenon and a critical modality in all kinds of sevicescapes. At restaurants, our senses are intensively stimulated. They are social places that depend on acoustic design for their success. Considering the large economic interests, surprisingly little empirical research on the psychoacoustics of restaurants is available. Contributing to theory building, this article proposes a typology of designed and non-designed sonic elements in restaurants. Results from a survey of 112 restaurants in Singapore are presented, with a focus on one element of the typology, namely interior design materials. The collected data included on-site sound level, audio recordings from which psychoacoustic descriptors such as Loudness and Sharpness were calculated, perceptual ratings using the Swedish Soundscape Quality protocol, and annotations of physical features such as Occupancy. We have introduced a measure, Priciness, to compare menu cost levels between the surveyed restaurants. Correlation analysis revealed several patterns: for example, that Priciness was negatively correlated with Loudness. Analysis of annotations of interior design materials supported a classification of the restaurants in categories of Design Style and Food Style. These were investigated with MANOVA, revealing significant differences in psychoacoustic, physical, and perceptual features between categories among the surveyed restaurants: for example, that restaurants serving Chinese food had the highest prevalence of stone materials, and that Western-menu places were the least loud. Some implications for managers, acoustic designers, and researchers are discussed. © 2015 Elsevier Ltd. All rights reserved.


Changizi S.A.,KTH Royal Institute of Technology | Qi C.,KTH Royal Institute of Technology | Wyss R.,KTH Royal Institute of Technology
Nuclear Physics A | Year: 2015

The empirical pairing gaps derived from four different odd-even mass staggering formulas are compared. By performing single-j shell and multi-shell seniority model calculations as well as by using the standard HFB approach with Skyrme force we show that the simplest three-point formula δC(3)(N)=12[B(N,Z)+B(N-2,Z)-2B(N-1,Z)] can provide a good measure of the neutron pairing gap in even-N nuclei. It removes to a large extent the contribution from the nuclear mean field as well as contributions from shell structure details. It is also less contaminated by the Wigner effect for nuclei around N=Z. We also show that the strength of δC(3)(N) can serve as a good indication of the two-particle spatial correlation in the nucleus of concern and that the weakening of δC(3)(N) in some neutron-rich nuclei indicates that the di-neutron correlation itself is weak in these nuclei. © 2015 Elsevier B.V..


Lapenta G.,Catholic University of Leuven | Markidis S.,KTH Royal Institute of Technology | Goldman M.V.,University of Colorado at Boulder | Newman D.L.,University of Colorado at Boulder
Nature Physics | Year: 2015

The primary target of the Magnetospheric MultiScale (MMS) mission is the electron-scale diffusion layer around reconnection sites. Here we study where these regions are found in full three-dimensional simulations. In two dimensions the sites of electron diffusion, defined as the regions where magnetic topology changes and electrons move with respect to the magnetic field lines, are located near the reconnection site. But in three dimensions we find that the reconnection exhaust far from the primary reconnection site also becomes host to secondary reconnection sites. Four diagnostics are used to demonstrate the point: the direct observation of topology impossible without secondary reconnection, the direct measurement of topological field line breakage, the measurement of electron jets emerging from secondary reconnection regions, and the violation of the frozen-in condition. We conclude that secondary reconnection occurs in a large part of the exhaust, providing many more chances for MMS to find itself in the right region to hit its target. © 2015 Macmillan Publishers Limited.


Jebari K.,KTH Royal Institute of Technology
Neuroethics | Year: 2013

Brain machine interface (BMI) technology makes direct communication between the brain and a machine possible by means of electrodes. This paper reviews the existing and emerging technologies in this field and offers a systematic inquiry into the relevant ethical problems that are likely to emerge in the following decades. © 2013 Springer Science+Business Media Dordrecht.


Forchheimer D.,KTH Royal Institute of Technology | Forchheimer R.,Linköping University | Haviland D.B.,KTH Royal Institute of Technology
Nature Communications | Year: 2015

Atomic force microscopy has recently been extented to bimodal operation, where increased image contrast is achieved through excitation and measurement of two cantilever eigenmodes. This enhanced material contrast is advantageous in analysis of complex heterogeneous materials with phase separation on the micro or nanometre scale. Here we show that much greater image contrast results from analysis of nonlinear response to the bimodal drive, at harmonics and mixing frequencies. The amplitude and phase of up to 17 frequencies are simultaneously measured in a single scan. Using a machine-learning algorithm we demonstrate almost threefold improvement in the ability to separate material components of a polymer blend when including this nonlinear response. Beyond the statistical analysis performed here, analysis of nonlinear response could be used to obtain quantitative material properties at high speeds and with enhanced resolution. © 2015 Macmillan Publishers Limited. All rights reserved.


O'Reilly C.J.,KTH Royal Institute of Technology
Applied Acoustics | Year: 2015

Acoustic liners are used extensively in engineering applications, particularly in aero-engines and automotive exhaust systems. In this paper, a flow impedance boundary conditions is introduced into the wave expansion method with the aim of providing an efficient methodology for computing the acoustic propagation through a lined duct with flow. For a potential flow, the boundary layer and the lined wall are included in the discretisation scheme by the Myers flow impedance boundary condition. The acoustic propagation through a flow impedance tube is computed in order to validate the implementation of the impedance boundary condition in this scheme. The results show that this computationally light methodology provides generally good agreement with the experimental data. © 2014 Elsevier Ltd. All rights reserved.


Heisenberg L.,KTH Royal Institute of Technology | Heisenberg L.,The Oskar Klein Center
Classical and Quantum Gravity | Year: 2015

We compute the one-loop quantum corrections to the interactions between the two metrics of the ghost-free massive bigravity. When considering gravitons running in the loops, we show how the structure of the interactions gets destabilized at the quantum level, exactly in the same way as in its massive gravity limit. A priori one might have expected a better quantum behavior, however, the broken diffeomorphism invariance out of the two initial diffeomorphisms in bigravity has similar consequences at the quantum level as the broken diffeomorphism in massive gravity. From lessons of the generated quantum corrections through matter loops we propose yet other types of effective composite metrics to which the matter fields can couple. Among these new effective metrics there might be one or more that could provide interesting phenomenology and important cosmological implications. © 2015 IOP Publishing Ltd.


Boden H.,KTH Royal Institute of Technology
Journal of Sound and Vibration | Year: 2012

Single sided multi-port system identification techniques, using sinusoidal excitation, for studying nonlinear energy transfer to higher harmonics for samples only accessible from one side such as perforated liners used as wall treatment in aircraft engine ducts are presented. The starting point is the so called polyharmonic distortion theory used for studying microwave systems. Models of different level of complexity are developed and the system identification results are compared. Experimental results, including error analysis, for a perforate sample are presented. The use of these techniques for analysing nonlinear energy transfer to higher harmonics and to improve the understanding of the physical phenomena involved are illustrated. © 2012 Elsevier Ltd. All rights reserved.


Gustafsson M.,Lund University | Cismasu M.,Lund University | Jonsson B.L.G.,KTH Royal Institute of Technology
IEEE Transactions on Antennas and Propagation | Year: 2012

Physical bounds on the directivity Q-factor quotient and optimal current distributions are determined for antennas of arbitrary shape and size using an optimization formulation. A variational approach offers closed form solutions for small antennas expressed in the polarizability of the antenna structure. Finite sized antennas are solved using Lagrangian parameters in a method of moments formulation. It is also shown that the optimal charge density for a small antenna can be generated by several current densities. Numerical examples for small and large antennas are used to illustrate the results. © 1963-2012 IEEE.


Hendriks R.C.,Technical University of Delft | Gerkmann T.,KTH Royal Institute of Technology
IEEE Transactions on Audio, Speech and Language Processing | Year: 2012

For multi-channel noise reduction algorithms like the minimum variance distortionless response (MVDR) beamformer, or the multi-channel Wiener filter, an estimate of the noise correlation matrix is needed. For its estimation, it is often proposed in the literature to use a voice activity detector (VAD). However, using a VAD the estimated matrix can only be updated in speech absence. As a result, during speech presence the noise correlation matrix estimate does not follow changing noise fields with an appropriate accuracy. This effect is further increased, as in nonstationary noise voice activity detection is a rather difficult task, and false-alarms are likely to occur. In this paper, we present and analyze an algorithm that estimates the noise correlation matrix without using a VAD. This algorithm is based on measuring the correlation of the noisy input and a noise reference which can be obtained, e.g., by steering a null towards the target source. When applied in combination with an MVDR beamformer, it is shown that the proposed noise correlation matrix estimate results in a more accurate beamformer response, a larger signal-to-noise ratio improvement and a larger instrumentally predicted speech intelligibility when compared to competing algorithms such as the generalized sidelobe canceler, a VAD-based MVDR beamformer, and an MVDR based on the noisy correlation matrix. © 2011 IEEE.


Walther A.,Aalto University | Bjurhager I.,KTH Royal Institute of Technology | Malho J.-M.,Aalto University | Pere J.,VTT Technical Research Center of Finland | And 3 more authors.
Nano Letters | Year: 2010

Although remarkable success has been achieved to mimic the mechanically excellent structure of nacre in laboratory-scale models, it remains difficult to foresee mainstream applications due to time-consuming sequential depositions or energy-intensive processes. Here, we introduce a surprisingly simple and rapid methodology for large-area, lightweight, and thick nacre-mimetic films and laminates with superior material properties. Nanoclay sheets with soft polymer coatings are used as ideal building blocks with intrinsic hard/soft character. They are forced to rapidly self-assemble into aligned nacre-mimetic films via paper-making, doctor-blading or simple painting, giving rise to strong and thick films with tensile modulus of 45 GPa and strength of 250 MPa, that is, partly exceeding nacre. The concepts are environmentally friendly, energy-efficient, and economic and are ready for scale-up via continuous roll-to-roll processes. Excellent gas barrier properties, optical translucency, and extraordinary shape-persistent fire-resistance are demonstrated. We foresee advanced large-scale biomimetic materials, relevant for lightweight sustainable construction and energy-efficient transportation. © 2010 American Chemical Society.


Silaev M.,KTH Royal Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

Magnetic properties of dirty multiband superconductors near the upper critical field are studied. The parameter κ2 characterizing magnetization slope is shown to have a significant temperature variation which is quite sensitive to the pairing interactions and relative strengths of intraband impurity scattering. In contrast to single-band superconductors the increase of κ2 at low temperatures can be arbitrarily large determined by the ratio of maximal and minimal diffusion coefficients in different bands. Temperature dependencies of κ2(T) in two-band MgB2 and iron-based superconductors are shown to be much more sensitive to the multiband effects than the upper critical field Hc2(T). © 2016 American Physical Society.


Krikun A.,KTH Royal Institute of Technology | Krikun A.,Institute of Theoretical and Experimental Physics
Journal of High Energy Physics | Year: 2014

We report the observation of the spatially modulated static mode in the spectrum of fluctuations around the condensed phase of the holographic d-wave superconductor. The mode involves the time component of the gauge field that is related to the charge density wave in the dual superconductor. No additional ingredients are added to the action of four dimensional theory. We speculate on the relevance of the observed mode to the formation of the pseudogap state. © The Authors.


Anderson L.,Chalmers University of Technology | Zarembo K.,KTH Royal Institute of Technology | Zarembo K.,Uppsala University
Journal of High Energy Physics | Year: 2014

Abstract: When mass-deformed ABJM theory is considered on S3, the partition function of the theory localises, and is given by a matrix model. At large N, we solve this model in the decompactification limit, where the radius of the three-sphere is taken to infinity. In this limit, the theory exhibits a rich phase structure with an infinite number of third-order quantum phase transitions, accumulating at strong coupling. © 2014, The Author(s).


Valenta J.,Charles University | Bruhn B.,KTH Royal Institute of Technology | Linnros J.,KTH Royal Institute of Technology
Nano Letters | Year: 2011

Single silicon nanowires (Si-NWs) prepared by electron-beam lithography and reactive-ion etching are investigated by imaging optical spectroscopy under variable temperatures and laser pumping intensities. Spectral images of individual Si-NWs reveal a large variability of photoluminescence (PL) along a single Si-NW. The weaker broad emission band asymmetrically extended to the high-energy side is interpreted to be due to recombination of quasi-free 1D excitons while the brighter localized emission features (with significantly variable peak position, width, and shape) are due to localization of electron-hole pairs in surface protrusions acting like quasi-0D centers or quantum dots (QDs). Correlated PL and scanning electron microscopy images indicate that the efficiently emitting QDs are located at the Si-NW interface with completely oxidized neck of the initial Si wall. Theoretical fitting of the delocalized PL emission band explains its broad asymmetrical band to be due to the Gaussian size distribution of the Si-NW diameter and reveals also the presence of recombination from the Si-NW excited state which can facilitate a fast capture of excitons into QD centers. © 2011 American Chemical Society.


Persson M.,KTH Royal Institute of Technology | Bornefalk H.,KTH Royal Institute of Technology
IEEE Transactions on Medical Imaging | Year: 2012

One of the challenges in the development of photon counting spectral computed tomography (CT) detectors is that the location of the energy thresholds tends to vary among detector elements. If not compensated for, this threshold variation leads to ring artifacts in the reconstructed images. In this paper, a framework is presented for the systematic comparison of different methods of compensating for inhomogeneities among detector elements in photon counting CT with multiple energy bins. Furthermore, we propose the use of an affine minimum mean square error estimator, calibrated against transmission measurements on different combinations of two materials, for inhomogeneity compensation. Using the framework developed here, this method is compared to two other compensation schemes, flatfielding using an air scan and signal-to-thickness calibration using a step wedge calibrator, in a simulation study. The results show that for all but the lowest studied level of threshold spread, the proposed method is superior to signal-to-thickness calibration, which in turn is superior to flatfielding. We also demonstrate that the effects of threshold variation can be countered to a large extent by substructuring each detector element into depth segments. © 1982-2012 IEEE.


Heisenberg L.,KTH Royal Institute of Technology | Heisenberg L.,The Oskar Klein Center
Journal of Cosmology and Astroparticle Physics | Year: 2015

In the context of massive gravity, bi-gravity and multi-gravity non-minimal matter couplings via a specific composite effective metric were investigated recently. Even if these couplings generically reintroduce the Boulware-Deser ghost, this composite metric is unique in the sense that the ghost reemerges only beyond the decoupling limit and the matter quantum loop corrections do not detune the potential interactions. We consider non-minimal derivative couplings of the composite metric to matter fields for a specific subclass of Horndeski scalar-tensor interactions. We first explore these couplings in the mini-superspace and investigate in which scenario the ghost remains absent. We further study these non-minimal derivative couplings in the decoupling-limit of the theory and show that the equation of motion for the helicity-0 mode remains second order in derivatives. Finally, we discuss preliminary implications for cosmology.


Ong Y.C.,KTH Royal Institute of Technology
General Relativity and Gravitation | Year: 2015

Classically, black holes admit maximal interior volumes that grow asymptotically linearly in time. We show that such volumes remain large when Hawking evaporation is taken into account. Even if a charged black hole approaches the extremal limit during this evolution, its volume continues to grow; although an exactly extremal black hole does not have a “large interior”. We clarify this point and discuss the implications of our results to the information loss and firewall paradoxes. © 2015, Springer Science+Business Media New York.


Koivisto T.S.,KTH Royal Institute of Technology | Urban F.R.,Free University of Colombia
Journal of Cosmology and Astroparticle Physics | Year: 2015

The Maxwell action is conformally invariant and classically ignorant of conformally flat metrics. However, if the vector lives in a disformal metric - as it does if residing upon a moving brane - this is no longer true. The disformal coupling is then mediated by a Dirac-Born-Infeld scalar field. Here a systematic dynamical system analysis is developed for anisotropic Bianchi I cosmology with a massive disformally coupled vector field. Several new fixed points are found, including anisotropic scaling solutions. The formalism here presented can be conveniently applied to general scenarios with or without extra dimensional motivations. This is illustrated here by performing a complete analysis with the assumption that both the potentials and the warp factor for the brane are (nearly) exponential. In that case, the anisotropic fixed points are either not attractors, do not describe accelerating expansion or else they feature too large anisotropies to be compatible with observations. Nonetheless, viable classes of models exist where isotropy is retained due to rapid oscillations of the vector field, thus providing a possible realisation of disformally interacting massive dark matter. © 2015 IOP Publishing Ltd and Sissa Medialab srl .


Heisenberg L.,KTH Royal Institute of Technology | Heisenberg L.,The Oskar Klein Center
Journal of Cosmology and Astroparticle Physics | Year: 2015

In this work we study the theory of extended quasidilaton massive gravity together with the presence of matter fields. After discussing the homogeneous and isotropic fully dynamical background equations, which governs the exact expansion history of the universe, we consider small cosmological perturbations around these general FLRW solutions. The stability of tensor, vector and scalar perturbations on top of these general background solutions give rise to slightly different constraints on the parameters of the theory than those obtained in the approximative assumption of the late-time asymptotic form of the expansion history, which does not correspond to our current epoch. This opens up the possibility of stable FLRW solutions to be compared with current data on cosmic expansion with the restricted parameter space based on theoretical ground.


Ong Y.C.,KTH Royal Institute of Technology
Journal of Cosmology and Astroparticle Physics | Year: 2015

Christodoulou and Rovelli have shown that black holes have large interiors that grow asymptotically linearly in advanced time, and speculated that this may be relevant to the information loss paradox. We show that there is no simple relation between the interior volume of an arbitrary black hole and its horizon area. That is, the volume enclosed is not necessarily a monotonically increasing function of the surface area. © 2015 IOP Publishing Ltd and Sissa Medialab srl.


Qi C.,KTH Royal Institute of Technology
Journal of Physics G: Nuclear and Particle Physics | Year: 2015

It is becoming increasingly important to understand the uncertainties of nuclear mass model calculations and their limitations when extrapolating to driplines. In this paper we evaluate the parameter uncertainties of the Duflo-Zuker (DZ) shell model mass formulae by fitting to the latest experimental mass compilation AME2012 using the least square and minimax fitting procedures. We also analyze the propagation of the uncertainties in binding energy calculations when extrapolated to driplines. The parameter uncertainties and uncertain propagations are evaluated with the help of the covariance matrix thus derived. Large deviations from the extrapolations of AME2012 are seen in superheavy nuclei. A simplified version of the DZ model (DZ19) with much smaller uncertainties than that of DZ33 is proposed. Calculations are compared with results from other mass formulae. Systematics on the uncertainty propagation as well as the positions of the driplines are also presented. The DZ mass formulae are shown to be well defined with good extrapolation properties and rather small uncertainties, even though some of the parameters of the full DZ33 model cannot be fully determined by fitting to available experimental data. © 2015 IOP Publishing Ltd.


Ringstrom H.,KTH Royal Institute of Technology
Classical and Quantum Gravity | Year: 2015

The seminal work of Yvonne Choquet-Bruhat published in 1952 demonstrates that it is possible to formulate Einstein's equations as an initial value problem. The purpose of this article is to describe the background to and impact of this achievement, as well as the result itself. In some respects, the idea of viewing the field equations of general relativity as a system of evolution equations goes back to Einstein himself; in an argument justifying that gravitational waves propagate at the speed of light, Einstein used a special choice of coordinates to derive a system of wave equations for the linear perturbations on a Minkowski background. Over the following decades, Hilbert, de Donder, Lanczos, Darmois and many others worked to put Einstein's ideas on a more solid footing. In fact, the issue of local uniqueness (giving a rigorous justification for the statement that the speed of propagation of the gravitational field is bounded by that of light) was already settled in the 1930s by the work of Stellmacher. However, the first person to demonstrate both local existence and uniqueness in a setting in which the notion of finite speed of propagation makes sense was Yvonne Choquet-Bruhat. In this sense, her work lays the foundation for the formulation of Einstein's equations as an initial value problem. Following a description of the results of Choquet-Bruhat, we discuss the development of three research topics that have their origin in her work. The first one is local existence. One reason for addressing it is that it is at the heart of the original paper. Moreover, it is still an active and important research field, connected to the problem of characterizing the asymptotic behaviour of solutions that blow up in finite time. As a second topic, we turn to the questions of global uniqueness and strong cosmic censorship. These questions are of fundamental importance to anyone interested in justifying that the Cauchy problem makes sense globally. They are also closely related to the issue of singularities in general relativity. Finally, we discuss the topic of stability of solutions to Einstein's equations. This is not only an important and active area of research, it is also one that only became meaningful thanks to the work of Yvonne Choquet-Bruhat. © 2015 IOP Publishing Ltd.


Rapp O.,KTH Royal Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

The zero-temperature conductivity σ(0) of icosahedral (i)-AlPdRe has been found to be simply related to the resistance ratio R=ρ4.2K/ρ295K by a power law, σ(0)∼R-1.74, over four orders of magnitude in σ(0). This relation includes metallic single grain samples, and polygrain samples of different morphologies which are metallic for small R values, and insulatinglike at large R. Electronic transport properties of single grain i-AlPdRe samples are thus found to be on common ground with polygrain i-AlPdRe. The relation between R and σ(0) can be qualitatively understood from published band-structure calculations on quasicrystalline approximants. © 2016 American Physical Society.


Larsson P.-L.,KTH Royal Institute of Technology
Journal of Applied Mechanics, Transactions ASME | Year: 2012

The effect of particle size distribution in powder compaction has been studied using the discrete element method. Both isostatic compaction and closed die compaction are studied together during the entire loading process. Particle rotation and frictional effects are accounted for in the analysis. The particles are, constitutively described by rigid plasticity, assumed to be spherical with the size of the radii that follows a truncated normal distribution. The results show that size distribution effects are small on global compaction properties like compaction pressure if the size distribution is small. Furthermore, the size distribution had no influence at all on the macroscopic behavior at unloading. To verify the model, comparisons were made on two different sets of experiment found in the literature where the particles were of varying sizes. Good agreement was found both on fundamental properties like the average number of contacts per particle and on more important properties from a practical point of view, like the compaction pressure. © 2012 American Society of Mechanical Engineers.


Schlatter P.,KTH Royal Institute of Technology | Orlu R.,KTH Royal Institute of Technology
Journal of Fluid Mechanics | Year: 2012

A recent assessment of available direct numerical simulation (DNS) data from turbulent boundary layer flows (Schlatter & Örlü, J. Fluid Mech., vol. 659, 2010, pp. 116-126) showed surprisingly large differences not only in the skin friction coefficient or shape factor, but also in their predictions of mean and fluctuation profiles far into the sublayer. While such differences are expected at very low Reynolds numbers and/or the immediate vicinity of the inflow or tripping region, it remains unclear whether inflow and tripping effects explain the differences observed even at moderate Reynolds numbers. This question is systematically addressed by re-simulating the DNS of a zero-pressure-gradient turbulent boundary layer flow by Schlatter et al. (Phys. Fluids, vol. 21, 2009, art. 051702). The previous DNS serves as the baseline simulation, and the new DNS with a range of physically different inflow conditions and tripping effects are carefully compared. The downstream evolution of integral quantities as well as mean and fluctuation profiles is analysed, and the results show that different inflow conditions and tripping effects do indeed explain most of the differences observed when comparing available DNS at low Reynolds number. It is further found that, if transition is initiated inside the boundary layer at a low enough Reynolds number (based on the momentum-loss thickness) Reθ> 300, all quantities agree well for both inner and outer layer for Reθ> 2000$. This result gives a lower limit for meaningful comparisons between numerical and/or wind tunnel experiments, assuming that the flow was not severely over- or understimulated. It is further shown that even profiles of the wall-normal velocity fluctuations and Reynolds shear stress collapse for higher Re θ> irrespective of the upstream conditions. In addition, the overshoot in the total shear stress within the sublayer observed in the DNS of Wu & Moin (Phys. Fluids, vol. 22, 2010, art. 085105) has been identified as a feature of transitional boundary layers. Copyright © 2012 Cambridge University Press.


Zeil P.,KTH Royal Institute of Technology | Thilmann N.,KTH Royal Institute of Technology | Pasiskevicius V.,KTH Royal Institute of Technology | Laurell F.,KTH Royal Institute of Technology
Optics Express | Year: 2014

A continuous-wave singly-resonant optical parametric oscillator (SRO) with an optimum extraction efficiency, that can be adjusted independent of the pump power, is demonstrated. The scheme employs a variable-reflectivity volume Bragg grating (VBG) as the output coupler of a ring cavity, omitting any additional intra-cavity elements. In this configuration, we obtained a 75%-efficient SRO with a combined signal (19 W @ 1.55 μm) and idler (11 W @ 3.4 μm) output power of 30 W. © 2014 Optical Society of America.


Edvardsson Bjornberg K.,KTH Royal Institute of Technology
Energy Policy | Year: 2013

The overall goal of the UNFCCC is to prevent dangerous anthropogenic interference with the climate system. In policy practice, this goal is mainly operationalized through three types of mitigation targets: emission, atmospheric concentration and temperature targets. The typical function of climate mitigation goals is to regulate action towards goal achievement. This is done in several ways. Mitigation goals help the structuring of the greenhouse gas (GHG) abatement action, over time and between agents; they constitute a standard against which GHG abatement can be assessed and evaluated; they motivate climate conscious behavior; and discourage defection from cooperative abatement regimes. Although the three targets clearly relate to one another, there could be differences in how well they fulfill these functions. In this article, the effectiveness of emission, concentration and temperature targets in guiding and motivating action towards the UNFCCC's overall aim is analyzed using a framework for rational goal evaluation developed by Edvardsson and Hansson (2005) as an analytical tool. It is argued that to regulate action effectively, mitigation goals should ideally satisfy four criteria: precision, evaluability, attainability and motivity. Only then can the target fulfill its typical function, i.e., to guide and motivate action in a way that facilitates goal achievement. © 2013 Elsevier Ltd.


Martensson J.,KTH Royal Institute of Technology | Hjalmarsson H.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

Solutions to optimal input design problems for system identification are sometimes believed to be sensitive to the underlying assumptions. For example, a wide class of problems can be solved with sinusoidal inputs with the same number of excitation frequencies (over the frequency range (-π ,π ] as the number of model parameters. The order of the true system is in many cases unknown and, hence, so is the required number of frequencies in the input. In this contribution we characterize when and how the input spectrum can be chosen so that the (asymptotic) variance error of a scalar function of the model parameters becomes independent of the order of the true system. A connection between these robust designs and the solutions of certain optimal input design problems is also made. Furthermore, we show that there are circumstances when using this type of input allows some model properties to be estimated consistently even when the model order is lower than the order of the true system. The results are derived under the assumptions of causal linear time invariant systems operating in open loop and excited by an input signal having a rational spectral factor with all poles and zeros strictly inside the unit circle. © 2010 IEEE.


Bao L.,KTH Royal Institute of Technology | Skoglund M.,KTH Royal Institute of Technology | Johansson K.H.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

We study a closed-loop control system with state feedback transmitted over a noisy discrete memoryless channel. With the objective to minimize the expected linear quadratic cost over a finite horizon, we propose a joint design of the sensor measurement quantization, channel error protection, and controller actuation. It is argued that despite that this encoder-controller optimization problem is known to be hard in general, an iterative design procedure can be derived in which the controller is optimized for a fixed encoder, then the encoder is optimized for a fixed controller, etc. Several properties of such a scheme are discussed. For a fixed encoder, we study how to optimize the controller given that full or partial side-information is available at the encoder about the symbols received at the controller. It is shown that the certainty equivalence controller is optimal when the encoder is optimal and has full side-information. For a fixed controller, expressions for the optimal encoder are given and implications are discussed for the special cases when process, sensor, or channel noise is not present. Numerical experiments are carried out to demonstrate the performance obtained by employing the proposed iterative design procedure and to compare it with other relevant schemes. © 2006 IEEE.


Alpcan T.,TU Berlin | Buchegger S.,KTH Royal Institute of Technology
IEEE Transactions on Mobile Computing | Year: 2011

Vehicular networks (VANETs) can be used to improve transportation security, reliability, and management. This paper investigates security aspects of VANETs within a game-theoretic framework where defensive measures are optimized with respect to threats posed by malicious attackers. The formulations are chosen to be abstract on purpose in order to maximize applicability of the models and solutions to future systems. The security games proposed for vehicular networks take as an input centrality measures computed by mapping the centrality values of the car networks to the underlying road topology. The resulting strategies help locating most valuable or vulnerable points (e.g., against jamming) in vehicular networks. Thus, optimal deployment of traffic control and security infrastructure is investigated both in the static (e.g., fixed roadside units) and dynamic cases (e.g., mobile law enforcement units). Multiple types of security games are studied under varying information availability assumptions for the players, leading to fuzzy game and fictitious play formulations in addition to classical zero-sum games. The effectiveness of the security game solutions is evaluated numerically using realistic simulation data obtained from traffic engineering systems. © 2011 IEEE.


Miron C.,Synchrotron Soleil | Nicolas C.,Synchrotron Soleil | Travnikova O.,Synchrotron Soleil | Morin P.,Synchrotron Soleil | And 4 more authors.
Nature Physics | Year: 2012

Electron-density distributions and potential-energy surfaces are important for predicting the physical properties and chemical reactivity of molecular systems. Whereas angle-resolved photoelectron spectroscopy enables the reconstruction of molecular-orbital densities of condensed species, absorption or traditional photoelectron spectroscopy are widely employed to study molecular potentials of isolated species. However, the information they provide is often limited because not all vibrational substates are excited near the vertical electronic transitions from the ground state. Moreover, many electronic states cannot be observed owing to selection rules or low transition probabilities. In many other cases, the extraction of the potentials is impossible owing to the high densities of overlapping electronic states. Here we use resonant photoemission spectroscopy, where the absence of strict dipole selection rules in Auger decay enables access to a larger number of final states as compared with radiative decay. Furthermore, by populating highly excited vibrational substates in the intermediate core-excited state, it is possible to 'pull out' molecular states that were hidden by overlapping spectral regions before. © 2012 Macmillan Publishers Limited. All rights reserved.


Baard P.,KTH Royal Institute of Technology
Journal of Risk Research | Year: 2014

Social decision-making involving risks ideally results in obligations to avoid expected harms or keep them within acceptable limits. Ambitious goals aimed at avoiding or greatly reducing risks might not be feasible, forcing the acceptance of higher degrees of risk (i.e. unrealistic levels of risk reduction are revised to comport with beliefs regarding abilities). In this paper, the philosophical principle ‘ought implies can’ is applied to the management of complex risks, exemplified by the risks associated with climate change. In its common interpretation, the principle states that we cannot expect an agent to perform something that lies beyond his or her abilities. However, it is here argued that this principle requires setting thresholds for legitimate claims of inabilities that justify the waiving of normative demands. This paper discuss three claims: (1) that caution is required before revising a risk-reducing goal that is perhaps exceedingly ambitious; (2) that claims on abilities are not only descriptive, but also value-laden; and (3) that the function of a goal has to be clarified before risk-reducing goals are revised. Risk-reducing goals that initially seem unrealistic arguably serve performance-enhancing purposes in risk management. Neglecting such goals could lead to choosing less desirable, but certainly feasible, risk-reducing goals. © 2014 Taylor & Francis


Moberg C.,KTH Royal Institute of Technology
Pure and Applied Chemistry | Year: 2016

In enantioselective reactions, the major, desired enantiomer is commonly obtained along with the minor, undesired enantiomer. By continuous recycling of this undesired enantiomer back to starting material, products with improved enantiomeric purity can be obtained. Such in situ minor enantiomer recycling can be accomplished by coupling the catalytic reaction to an exergonic transformation of a sacrificial reagent. The method has been applied to the synthesis of O-acylated cyanohydrins, which serve as starting materials for a variety of biologically active compounds. © 2016 IUPAC & De Gruyter.


Sun F.,Zhejiang University | He S.,KTH Royal Institute of Technology
Progress in Electromagnetics Research | Year: 2010

Both explicit analysis and FEM numerical simulation are used to analyze the field distribution of a line current in the so-called Maxwell's fish eye lens [bounded with a perfectly electrical conductor (PEC) boundary]. We show that such a 2D Maxwell's fish eye lens cannot give perfect imaging due to the fact that high order modes of the object field can hardly reach the image point in Maxwell's fish eye lens. If only zeroth order mode is excited, a good image of a sharp object may be achieved in some cases, however, its spot-size is larger than the spot size of the initial object field. The image resolution is determined by the field spot size of the image corresponding to the zeroth order component of the object field. Our explicit analysis consists very well with the FEM results for a fish eye lens. Time-domain simulation is also given to verify our conclusion. Multi-point images for a single object point are also demonstrated.


Hakkarainen M.,KTH Royal Institute of Technology
Advances in Polymer Science | Year: 2012

The stability and durability of polymeric materials under different external influences (e.g., sunlight, humidity, heat, chemicals, or microorganisms) is of outmost importance in applications such as coatings, building materials, and automotive parts, whereas a rapidly degradable material is preferable in temporary short-term applications. There are considerable economic and environmental benefits if we can design polymers for short or long lifetimes as well as prevent the release of harmful substances from the materials during their lifetime. The recent developments in mass spectrometric techniques facilitate possibilities for molecular level characterization of the changes taking place in the polymer matrix as well as for identification of the released degradation products. This review presents an overview of the application of electrospray ionization-mass spectrometry (ESI-MS) for the analysis of polymer degradation. The great potential of the technique for revealing detailed insights into the degradative reactions taking place is demonstrated with examples ranging from degradable polymers and biomaterials to degradation of coatings, paints, polymer electrolyte membranes, food packaging, and materials in the nuclear industry. © 2011 Springer-Verlag Berlin Heidelberg.


Lu H.,KTH Royal Institute of Technology | Alanne K.,Aalto University | Martinac I.,KTH Royal Institute of Technology
Energy Conversion and Management | Year: 2014

Renewable energy systems entail a significant potential to meet the energy requirements of building clusters and districts (BCDs) provided that local energy sources are exploited efficiently. Besides improving the energy efficiency by reducing energy consumption and improving the match between energy supply and demand, energy quality issues have become a key topic of interest. Energy quality management is a technique that aims at optimally utilizing the exergy content of various renewable energy sources. In addition to minimizing life-cycle CO2 emissions related to exergy losses of an energy system, issues such as system reliability should be addressed. The present work contributes to the research by proposing a novel multi-objective design optimization scheme that minimizes the global warming potential during the life-cycle and maximizes the exergy performance, while the maximum allowable level of the loss of power supply probability (LPSP) is predefined by the user as a constraint. The optimization makes use of Genetic Algorithm (GA). Finally, a case study is presented, where the above methodology has been applied to an office BCD located in Norway. The proposed optimization scheme is proven to be efficient in finding the optimal design and can be easily enlarged to encompass more relevant objective functions. © 2014 Elsevier Ltd. All rights reserved.


Huang S.,KTH Royal Institute of Technology
Proceedings of the Annual ACM Symposium on Theory of Computing | Year: 2013

We prove that for all integer k ≥ 3, there is a predicate P on k Boolean variables with 2 Õ (k1/3) accepting assignments that is approximation resistant even on satisiable instances. That is, given a satisfiable CSP instance with constraint P, we cannot achieve better approximation ratio than simply picking random assignments. This improves the best previously known result by Håstad and Khot where the predicate has 2O(k1/2) accepting assignments. Our construction is inspired by several recent developments. One is the idea of using direct sums to improve soundness of PCPs, developed by Chan [5]. We also use techniques from Wenner [32] to construct PCPs with perfect completeness without relying on the d-to-1 Conjecture. Copyright 2013 ACM.


Chen G.,State University of New York at Buffalo | Chen G.,KTH Royal Institute of Technology | Ohulchanskyy T.Y.,State University of New York at Buffalo | Kachynski A.,State University of New York at Buffalo | And 2 more authors.
ACS Nano | Year: 2011

We report intense upconversion photoluminescence (PL) in colloidal LiYF4:Er3+ nanocrystals under excitation with telecom-wavelength at 1490 nm. The intensities of two- and three-photon anti-Stokes upconversion PL bands are higher than or comparable to that of the Stokes emission under excitation with low power density in the range 5-120 W/cm2. The quantum yield of the upconversion PL was measured to be as high as ∼1.2 ± 0.1%, which is almost 4 times higher than the highest upconversion PL quantum yield reported to date for lanthanide-doped nanocrystals in 100 nm sized hexagonal NaYF4:Yb3+20%, Er3+2% using excitation at ∼980 nm. A power dependence study revealed that the intensities of all PL bands have linear dependence on the excitation power density, which was explained by saturation effects in the intermediate energy states. © 2011 American Chemical Society.


Zhang W.,Zhejiang University | Li Q.,Zhejiang University | Qiu M.,Zhejiang University | Qiu M.,KTH Royal Institute of Technology
Optics Express | Year: 2013

The determination of nanoscale distances or distance changes necessitates a nanoscale ruler. In the present paper, distance dependence of particle temperature in an optically heated gold nanoparticle pair is quantitatively investigated to explore the possibility of creating a Plasmon ruler based on this effect. The two origins of the distance-dependence, i.e., electromagnetic coupling and thermal accumulative effect, are studied. For the particle temperature, a scaling behavior is found, and it suggests that the decay of particle temperature with the interparticle gap for different particle sizes follows a common exponential decay equation. This scaling behavior is qualitatively explained with a simple dipolar-coupling model combined with a point heat source interaction model. On the basis of this scaling behavior of absorption power, we further establish a plasmon ruler equation relating the particle temperature and the interparticle distance. Our findings can serve as an excellent guideline for designing and optimizing temperature-based plasmon rulers. © 2013 Optical Society of America.


Jaeken B.,University of Murcia | Lundstrom L.,KTH Royal Institute of Technology | Artal P.,University of Murcia
Optics Express | Year: 2011

We designed and built a fast scanning peripheral Hartmann-Shack (HS) wave-front sensor to measure the off-axis wave-front aberrations in the human eye. The new instrument is capable of measuring the optical quality over the central 80° horizontal visual field in 1.8 seconds with an angular resolution of 1°. The subject has an open field of view without any moving elements in the line-of-sight and the head is kept in place by a head-chin rest. The same efficiency, reliability and measurement quality as the current static HS sensor were found but with much higher acquisition speed and comfort for the patients. This instrument has the potential to facilitate and improve future research on the peripheral optical quality of the eye in large groups of subjects. © 2011 Optical Society of America.


Guan X.,Zhejiang University | Wu H.,Zhejiang University | Shi Y.,Zhejiang University | Wosinski L.,KTH Royal Institute of Technology | Dai D.,Zhejiang University
Optics Letters | Year: 2013

An ultracompact polarization beam splitter (PBS) is proposed based on an asymmetrical directional coupler consisting of a silicon hybrid plasmonic waveguide (HPW) and a silicon nanowire. The widths of the two coupling waveguides are chosen so that the phase-matching condition is satisfied for TE polarization only while the phase mismatch is significant for TM polarization. A sharply bent silicon HPW is connected at the thru port to play the role of polarizer by utilizing its polarization-dependent loss. With the present principle, the designed PBS has a footprint as small as only ∼1.9 μm × 3.7 μm, which is the shortest PBS reported until now, even when large waveguide dimensions (e.g., the waveguide widths w1;2 = ∼300 nm and the gap width wgap = ∼200 nm) are chosen to simplify the fabrication process. The numerical simulations show that the designed PBS has a very broad band (∼120 nm) with an extinction ratio >12 dB and a large fabrication tolerance to allow a waveguide width variation of ±30 nm. © 2013 Optical Society of America.


Duguet Y.,CNRS Computer Science Laboratory for Mechanics and Engineering Sciences | Schlatter P.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2013

Localized structures such as turbulent stripes and turbulent spots are typical features of transitional wall-bounded flows in the subcritical regime. Based on an assumption for scale separation between large and small scales, we show analytically that the corresponding laminar-turbulent interfaces are always oblique with respect to the mean direction of the flow. In the case of plane Couette flow, the mismatch between the streamwise flow rates near the boundaries of the turbulence patch generates a large-scale flow with a nonzero spanwise component. Advection of the small-scale turbulent fluctuations (streaks) by the corresponding large-scale flow distorts the shape of the turbulence patch and is responsible for its oblique growth. This mechanism can be easily extended to other subcritical flows such as plane Poiseuille flow or Taylor-Couette flow. © 2013 American Physical Society.


Zhang L.,ABB | Harnefors L.,ABB | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2010

In this paper, a novel control method of grid-connected voltage-source converters (VSCs) is proposed. The method can be generally applied for all grid-connected VSCs but may be of most importance in high-voltage dc (HVDC) applications. Different from the previous control methods, the proposed method utilizes the internal synchronization mechanism in ac systems, in principle, similar to the operation of a synchronous machine. By using this type of power-synchronization control, the VSC avoids the instability caused by a standard phase-locked loop in a weak ac-system connection. Moreover, a VSC terminal can give the weak ac system strong voltage support, just like a normal synchronous machine does. The control method is verified by both analytical models and time simulations. © 2010 IEEE.


Guan T.,KTH Royal Institute of Technology | Alvfors P.,KTH Royal Institute of Technology | Lindbergh G.,KTH Royal Institute of Technology
Applied Energy | Year: 2014

A PEMFC fuelled with hydrogen is known for its high efficiency and low local emissions. However, the generation of hydrogen is always a controversial issue for the application of the PEMFC due to the use of fossil fuel and the possible carbon dioxide emissions. Presently, the PEMFC-CHP fed with renewable fuels, such as biogas, appears to be the most attractive energy converter-fuel combination. In this paper, an integrated PEMFC-CHP, a dairy farm and a biogas plant are studied. A PEMFC-CHP fed with reformate gas from the biogas plant generates electricity and heat to a dairy farm and a biogas plant, while the dairy farm delivers wet manure to the biogas plant as the feedstock for biogas production. This integrated system has been modelled for steady-state conditions by using Aspen Plus®. The results indicate that the wet manure production of a dairy farm with 300 milked cows can support a biogas plant to give 1280MWh of biogas annually. Based on the biogas production, a PEMFC-CHP with a stack having an electrical efficiency of 40% generates 360MWh electricity and 680MWh heat per year, which is enough to cover the energy demand of the whole system while the total efficiency of the PEMFC-CHP system is 82%. The integrated PEMFC-CHP, dairy farm and biogas plant could make the dairy farm and the biogas plant self-sufficient in a sustainable way provided the PEMFC-CHP has the electrical efficiency stated above. The effect of the methane conversion rate and the biogas composition on the system performance is discussed. Moreover, compared with the coal-fired CHP plant, the potentially avoided fossil fuel consumption and CO2 emissions of this self-sufficient system are also calculated. © 2014 Elsevier Ltd.


Carlstrom J.,KTH Royal Institute of Technology | Babaev E.,KTH Royal Institute of Technology | Babaev E.,University of Massachusetts Amherst | Speight M.,University of Leeds
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

In contrast to single-component superconductors, which are described at the level of Ginzburg-Landau theory by a single parameter κ and are divided in type-I κ<1/√2 and type-II κ1/√2 classes, two-component systems in general possess three fundamental length scales and have been shown to possess a separate "type-1.5" superconducting state. In that state, as a consequence of the extra fundamental length scale, vortices attract one another at long range but repel at shorter ranges, and therefore should form clusters in low magnetic fields. In this work we investigate the appearance of type-1.5 superconductivity and the interpretation of the fundamental length scales in the case of two active bands with substantial interband couplings such as intrinsic Josephson coupling, mixed gradient coupling, and density-density interactions. We show that in the presence of substantial intercomponent interactions of the above types the system supports type-1.5 superconductivity with fundamental length scales being associated with the mass of the gauge field and two masses of normal modes represented by mixed combinations of the density fields. © 2011 American Physical Society.


Zhang L.,ABB | Harnefors L.,ABB | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2011

The recently proposed power-synchronization control for grid-connected voltage-source converters (VSCs) has been shown to be a feasible solution for high-voltage direct-current (HVDC) transmission connected to high-impedance weak ac systems. In this paper, power-synchronization control is investigated for VSC-HVDC links connected to another type of weak ac system, i.e., low-inertia or island systems. As an example, a linear model of a typical island system feeding by a VSC-HVDC link, including a synchronous generator, an induction motor, and some passive loads, is developed for tuning the control parameters of the VSC-HVDC link. Time simulations in PSCAD/EMTDC demonstrate that VSC-HVDC systems using power-synchronization control are flexible for various network conditions, such as large-ac-system connection, island systems, or passive networks. The time simulations also show that power-synchronization control can seamlessly handle transitions between operation modes, as well as ride through ac-system faults in all network conditions. © 2010 IEEE.


Chenine M.,KTH Royal Institute of Technology | Nordstrom L.,KTH Royal Institute of Technology
IEEE Transactions on Power Delivery | Year: 2011

Phasor-based wide-area monitoring and control (WAMC) systems are becoming a reality with increased research, development, and deployments. Many potential control applications based on these systems are being proposed and researched. These applications are either local applications using data from one or a few phasor measurement units (PMUs) or centralized utilizing data from several PMUs. An aspect of these systems, which is less well researched, is the WAMC system's dependence on high-performance communication systems. This paper presents the results of research performed in order to determine the requirements of transmission system operators on the performance of WAMC systems in general as well as the characteristics of communication delays incurred in centralized systems that utilize multiple PMUs distributed over a large geographic area. This paper presents a summary of requirements from transmission system operators with regards to a specific set of applications and simulations of communication networks with a special focus on centralized applications. The results of the simulations indicate that the configuration of central nodes in centralized WAMC systems needs to be optimized based on the intended WAMC application. © 2011 IEEE.


Alvehag K.,KTH Royal Institute of Technology | Soder L.,KTH Royal Institute of Technology
IEEE Transactions on Power Delivery | Year: 2011

In distribution system planning and operation, accurate assessment of reliability performance is essential for making informed decisions. Also, performance-based regulation, accompanied by quality regulation, increases the need to understand and quantify differences in reliability performance between networks. Distribution system reliability performance indices exhibit stochastic behavior due to the impact of severe weather. In this paper, a new reliability model is presented which incorporates the stochastic nature of the severe weather intensity and duration to model variations in failure rate and restoration time. The model considers the impact of high winds and lightning and can be expanded to account for more types of severe weather. Furthermore, the modeling approach considers when severe weather is likely to occur during the year by using a nonhomogeneous Poisson process (NHPP). The proposed model is validated and applied to a test system to estimate reliability indices. Results show that the stochasticity in weather has a great impact on the variance in the reliability indices. © 2010 IEEE.


Johansson N.,KTH Royal Institute of Technology | Angquist L.,KTH Royal Institute of Technology | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2011

This paper compares four different methods for determining the electrical damping of a power system seen from one generator as a function of frequency. This information is useful when the risk for subsynchronous resonance (SSR) in the system is evaluated. The study compares one frequency scanning method which is implemented in a time-domain digital simulation program with three methods of different complexity based on analytical calculations. The time-domain simulation method is easily implemented with a detailed model of the power system including complex load and generator models, whereas the analytical methods are based on simpler models of the power system. The computational effort is much larger for the time-domain method than for the analytical methods. In the study, all methods were used to determine the damping characteristics of a four-machine power system in different configurations. The study shows that fast analytical methods may provide results which closely agree with the detailed method of time-domain simulation. However, the study also shows that the level of accuracy in the analytical model is very important. © 2010 IEEE.


Lapisa M.,KTH Royal Institute of Technology | Stemme G.,KTH Royal Institute of Technology | Niklaus F.,KTH Royal Institute of Technology
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2011

Wafer-level heterogeneous integration technologies for microoptoelectromechanical systems (MOEMS), microelectromechanical systems (MEMS), and nanoelectromechanical systems (NEMS) enable the combination of dissimilar classes of materials and components into single systems. Thus, high-performance materials and subsystems can be combined in ways that would otherwise not be possible, and thereby forming complex and highly integrated micro- or nanosystems. Examples include the integration of high-performance optical, electrical or mechanical materials such as monocrystalline silicon, graphene or III-V materials with integrated electronic circuits. In this paper the state-of-the-art of wafer-level heterogeneous integration technologies suitable for MOEMS, MEMS, and NEMS devices are reviewed. Various heterogeneous MOEMS, MEMS, and NEMS devices that have been described in literature are presented. © 2006 IEEE.


Terelius B.,KTH Royal Institute of Technology
Proceedings of the 2013 IEEE International Workshop on Information Forensics and Security, WIFS 2013 | Year: 2013

Buyer-seller watermarking protocols are protocols that let a seller embed a watermark which uniquely identifies the buyer of each sold copy of some work without allowing the seller to learn the watermark. The purpose of such protocols is to deter buyers from illegally redistributing the work while protecting the buyer from being framed by dishonest sellers. Existing buyer-seller watermarking schemes require that every buyer receives his or her copy directly from the seller. We consider the problem of extending buyer-seller watermarking to allow (controlled) redistribution between buyers while maintaining a watermark that uniquely identifies each recipient. An efficient and secure protocol of this type could allow distribution of digital content in peer-to-peer networks while protecting the owner's copyright. We give a proof-of-concept protocol which only requires limited interaction with the original seller to change the watermark. © 2013 IEEE.


Blom P.,KTH Royal Institute of Technology | Kari L.,KTH Royal Institute of Technology
Journal of Sound and Vibration | Year: 2011

A novel constitutive model of magneto-sensitive rubber in the audible frequency range is presented. Characteristics inherent to magneto-sensitive rubber within this dynamic regime are defined: magnetic sensitivity, amplitude dependence, elasticity and viscoelasticity. Prior to creating the model assumptions based on experimental observations concerning these components are formulated. The first observation is that not only does the rubber display a strong amplitude dependence even for small strains, but also the magnetic sensitivity is strongly amplitude dependent. The second and third are, respectively, that the elastic component is magneto-sensitive, whereas the viscoelastic dependence on magnetic induction appears to be small. Thus, the model is developed from these assumptions and parameters are optimized with respect to experimental values for one case and subsequently validated for others; a very good agreement is obtained. © 2010 Elsevier Ltd. All rights reserved.


Burenius M.,KTH Royal Institute of Technology | Sullivan J.,KTH Royal Institute of Technology | Carlsson S.,KTH Royal Institute of Technology
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2013

We consider the problem of automatically estimating the 3D pose of humans from images, taken from multiple calibrated views. We show that it is possible and tractable to extend the pictorial structures framework, popular for 2D pose estimation, to 3D. We discuss how to use this framework to impose view, skeleton, joint angle and intersection constraints in 3D. The 3D pictorial structures are evaluated on multiple view data from a professional football game. The evaluation is focused on computational tractability, but we also demonstrate how a simple 2D part detector can be plugged into the framework. © 2013 IEEE.


Vallgren A.,KTH Royal Institute of Technology
Journal of Fluid Mechanics | Year: 2011

High-resolution simulations of forced two-dimensional turbulence reveal that the inverse cascade range is sensitive to an infrared Reynolds number, Re = kf/k, where kf is the forcing wavenumber and k is a frictional wavenumber based on linear friction. In the limit of high Re, the classic k5/3 scaling is lost and we obtain steeper energy spectra. The sensitivity is traced to the formation of vortices in the inverse energy cascade range. Thus, it is hypothesized that the dual limit Re and Re = kd/kf, where kd is the small-scale dissipation wavenumber, will lead to a steeper energy spectrum than k 5/3 in the inverse energy cascade range. It is also found that the inverse energy cascade is maintained by non-local triad interactions. © 2011 Cambridge University Press.


Finnveden S.,KTH Royal Institute of Technology
Journal of Sound and Vibration | Year: 2011

The response of two general spring-coupled elements is investigated to develop a unifying approach to the weak coupling criterion in Statistical Energy Analysis (SEA). First, the coupled deterministic equations of motion are expressed in the bases given by the uncoupled elements' eigenmodes. Then, an iterative solution is expressed as a succession of exchanges between elements, where uncoupled motion provides the start approximation, converging if the 'coupling eigenvalue' is less than unity, in which case coupling is said to be weak. This definition is related to whether response is 'local' or 'global', encompassing a number of previously defined coupling strength definitions, applying for deterministically described structures. A stochastic ensemble is defined by that its members are equal to the investigated structure but the elements have random frequencies. It is required that the coupling eigenvalue be less than unity for all members of the ensemble. This requirement generates the title subject of the article: 'the modal interaction strength'. It is similar to the previously defined coupling strength criterion characterising the ensemble average energy flow in uni-dimensional waveguides. Finally, SEA models are formulated in terms of the uncoupled elements' modal data. © 2010 Elsevier Ltd.


Cats O.,KTH Royal Institute of Technology
Procedia Computer Science | Year: 2013

Transit systems exercise complex dynamics and evolve through the interaction of various agents. The analysis of transit performance requires emulating the dynamic loading of travellers and their interaction with the underlying transit system. Multi-agent simulations aim to mimic the emergence of global spontaneous order from numerous inter-dependent local decisions. This paper presents a framework for a multi-agent transit operations and assignment model which captures supply uncertainties and adaptive user decisions. An iterative day-to-day learning process consisting of a within-day dynamic network loading loop simulates the interaction between transit supply and demand. The model requires the development and integration of several modules including traffic simulation, transit operations and control, dynamic path choice model and real-time information generator. BusMezzo, a transit simulation model, is used as the platform for implementation. © 2013 The Authors. Published by Elsevier B.V.


HAkansson A.,KTH Royal Institute of Technology
Procedia Computer Science | Year: 2013

AI-complete systems developed today, are commonly used for solving different artificial intelligence problems. A problem is a typical image recognition or speech recognition, but it can also be language processing, as well as, other complex systems dealing with general problem solving. However, no AI-complete system, which models the human brain or behavior, can exist without looking at the totality of the whole situation and, and hence, incorporating an AI-computerized sensory systems into a totality that constitute a combination of senses. This paper proposes a combination of sensory systems to form a comprehensive AI-system by combining the different senses, called AIC-AI-system for a combination of senses. The AIC-system is not a complete system in the sense that it contains a total set of information or uses all kinds of digital sensory systems. Nonetheless, it is a system under self-development. It develops its own knowledge base, as experiences, which will be based on the different characteristics: images, sounds, smells, tastes, touches with emotions/feelings and expressions. The result is a kind of perception of the surrounding environment. © 2013 The Authors.


Kopsch F.,KTH Royal Institute of Technology
Journal of Air Transport Management | Year: 2012

This article analyses demand for domestic air travel in Sweden. Using aggregated data on passenger quantities and fares, price elasticities are estimated. The robustness of the results is enforced by simple division of business and leisure travellers. The analysis also includes estimates of cross-price elasticities for the main transport substitutes to air travel; rail and road. The results indicate that aggregated demand for domestic air travel in Sweden is fairly elastic in the short-run and more elastic in the long-run. The robustness test of the model show that leisure travellers are more sensitive to price changes than are business travellers. Further, the cross-price elasticity between rail and air travel is found to lie between 0.43 and 0.5. © 2011 Elsevier Ltd.


Levihn F.,KTH Royal Institute of Technology
Energy | Year: 2014

CO2 abatement and the transition to sustainable energy systems are of great concern, calling for investments in both old and new technologies. There are many perspectives on how to account for these emissions, not least when it comes to how the roles of different alternative energy production options should be emphasized. Confusion and conflicting interests regarding the appropriate accounting methods for allocating CO2 emissions interfere with effective energy policy and the efficient use of corporate and national resources. Possible investments in the Stockholm district heating network and how they interact with the electric power grid illustrate the influence of different accounting methods on alternative energy production options. The results indicate that, for several abatement options, performance in terms of reduced CO2 emissions might be either improved or degraded depending on whether or how alternative electricity production is accounted for. The results provide guidelines for whether, how, and when different allocation methods are appropriate, guidelines relevant to academia, industrial leaders, and policymakers in multiple areas related to power production and consumption. © 2014 Elsevier Ltd.


Alin J.,KTH Royal Institute of Technology | Hakkarainen M.,KTH Royal Institute of Technology
Journal of Agricultural and Food Chemistry | Year: 2011

Microwave heating of commercial microwavable polypropylene packaging in contact with fatty food simulants caused significant antioxidant degradation and increased specific migration as shown by electrospray ionization-mass spectrometry (ESI-MS) and gas chromatography-mass spectrometry (GC-MS). Degradation of the antioxidants Irgafos 168 and Irganox 1010 was not detected during conventional heating of polypropylene packaging at the same temperature. The migration into aqueous food simulants was primarily restricted by the water solubility of the migrants. Using isooctane as fatty food simulant caused significant swelling and greatly enhanced overall migration values compared to the other fatty food simulant, 99.9% ethanol, or the aqueous food simulants 10% ethanol, 3% acetic acid, or water. ESI-MS spectra clearly reflected the overall migration values, and the number and amount of compounds detected decreased as the hydrophilicity of the food simulant increased. ESI-MS was shown to be an excellent tool for the analysis of semivolatile migrants and a good complement to GC-MS analysis of volatile migrants. © 2011 American Chemical Society.


Liu A.,KTH Royal Institute of Technology | Berglund L.A.,KTH Royal Institute of Technology
Carbohydrate Polymers | Year: 2012

Clay nanopaper are nanocomposites with nacre-like structure and multifunctional characteristics including high modulus, significant strength and toughness as well as fire retardancy and low oxygen transmission rate (OTR). Montmorrilonite (MTM) and nanofibrillated cellulose (NFC) hydrocolloids are combined with a chitosan (CS) solution to form high MTM content nanopaper structures by the use of a previously developed papermaking approach. Chitosan functions as flocculation agent and decreases dewatering time to less than 10% compared with MTM-NFC clay nanopaper. The effect of chitosan on the clay nanopaper structure was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Properties were measured by uniaxial tensile testing, thermogravimetric analysis (TGA), OTR and moisture adsorption experiments. A nacre-like multilayered structure was confirmed and the chitosan-clay nanopaper showed favorable mechanical properties at clay contents as high as 44-48 wt%. © 2011 Published by Elsevier Ltd.


Kroon M.,KTH Royal Institute of Technology
Journal of Elasticity | Year: 2011

Several industrial applications involve rubber and rubber-like materials, and it is important to be able to predict the constitutive response of these materials. In the present paper, a new constitutive model for rubber-like solids is proposed. The model is based on the 8-chain concept introduced by Arruda and Boyce (J. Mech. Phys. Solids 41, 389-412, 1993) to which two new components are added. Real polymer networks do not deform affinely, and in the proposed model this is accounted for by the inclusion of an elastic spring, acting in series with the representative polymer chain. Furthermore, real polymer chains are not completely free to move, which is modelled by imposing a topological constraint on the transverse motions of the representative polymer chain. The model contains five model parameters and these need to be determined on the basis of experimental data. Three experimental studies from the literature were used to assess the proposed model. The model was able to reproduce experimental data performed under conditions of uniaxial tension, generalised plane deformation, and biaxial tension with an excellent accuracy. The strong predictive abilities together with the numerically efficient structure of the model make it suitable for implementation in a finite element context. © 2010 Springer Science+Business Media B.V.


Zhang L.,ABB | Harnefors L.,ABB | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2011

In this paper, voltage-source converter (VSC) based high-voltage dc (HVDC) transmission is investigated for interconnection of two very weak ac systems. By using the recently proposed power-synchronization control, the short-circuit capacities of the ac systems are no longer the limiting factors, but rather the load angles. For the analysis of the stability, the Jacobian transfer matrix concept has been introduced. The right-half plane (RHP) transmission zero of the ac Jacobian transfer matrix moves closer to the origin with larger load angles. The paper shows that, due to the bandwidth limitation imposed by the RHP zero on the direct-voltage control of the VSC, high dc-capacitance values are needed for such applications. In addition, the paper proposes a control structure particularly designed for weak-ac-system interconnections. As an example, it is shown that the proposed control structure enables a power transmission of 0.86 p.u. from a system with the short-circuit ratio (SCR) of 1.2 to a system with an SCR of 1.0. This should be compared to previous results for VSC based HVDC using vector current control. In this case, only 0.4 p.u. power transmission can be achieved for dc link where only one of the ac systems has an SCR of 1.0. © 2010 IEEE.


Perninge M.,KTH Royal Institute of Technology | Soder L.,KTH Royal Institute of Technology
Electric Power Systems Research | Year: 2011

Prevention of voltage instability in electric power systems is an important objective that the system operators have to meet. Under certain circumstances the operating point of the power system may start drifting towards the set of voltage unstable operating points. If no preventive measures are taken, after some time, the operating point may eventually become voltage unstable. It will thus be preferable to have a measure of the risk of voltage collapse in future loading states. This paper presents a novel method for estimation of the probability distribution of the load-space distance to the point where voltage instability induced by saddle-node bifurcation occurs. Another result of the method is an estimate of the probability distribution of the time to voltage instability for a power system with uncertain future loading scenarios. The method uses a second order approximation of the saddle-node bifurcation surface. The proposed method can be used in power system security assessments. © 2010 Elsevier B.V. All rights reserved.


Latorre H.F.,KTH Royal Institute of Technology | Ghandhari M.,KTH Royal Institute of Technology
International Journal of Electrical Power and Energy Systems | Year: 2011

The capabilities of a VSC-HVdc to improve the stability in power systems are analyzed in this paper. The analysis considers a power system which has the need for increasing the transmission capacity. Two options are analyzed: connection of a new ac transmission line or connection of a VSC-HVdc link. Different disturbances are applied in the system in order to analyze the dynamic response of the system. Supplementary control is included in the control of the VSC-HVdc. The control strategies in the supplementary control are based on nonlinear and linear theory. Furthermore, remote and local information are used as input signals in the control strategies. Simulation results clearly showed the benefits of VSC-HVdc in the improvement of power system stability. © 2010 Elsevier Inc. All rights reserved.


Svagan A.J.,KTH Royal Institute of Technology | Berglund L.A.,KTH Royal Institute of Technology | Jensen P.,National Museum Denmark
ACS Applied Materials and Interfaces | Year: 2011

Starch is an attractive biofoam candidate as replacement of expanded polystyrene (EPS) in packaging materials. The main technical problems with starch foam include its hygroscopic nature, sensitivity of its mechanical properties to moisture content, and much lower energy absorption than EPS. In the present study, a starch-based biofoam is for the first time able to reach comparable mechanical properties (E = 32 MPa, compressive yield strength, 630 kPa) to EPS at 50% relative humidity and similar relative density. The reason is the nanocomposite concept in the form of a cellulose nanofiber network reinforcing the hygroscopic amylopectin starch matrix in the cell wall. The biofoams are prepared by the freezing/freeze-drying technique and subjected to compressive loading. Cell structure is characterized by FE-SEM of cross sections. Mechanical properties are related to cell structure and cell wall nanocomposite composition. Hierarchically structured biofoams are demonstrated to be interesting materials with potential for strongly improved mechanical properties. © 2011 American Chemical Society.


Sehaqui H.,KTH Royal Institute of Technology | Zhou Q.,Albanova University Center | Berglund L.A.,KTH Royal Institute of Technology
Composites Science and Technology | Year: 2011

Low-density aerogels based on nanofibrillated cellulose (NFC) from wood pulp were prepared from NFC aqueous dispersions using solvent exchange from water to tert-butanol followed by tert-butanol freeze-drying. In the present study, the dispersion of NFC nanofibers in the hydrocolloid was very well preserved in the aerogels. The " effective" diameter of the NFC nanofibers in the aerogels is around 10-18nm corresponding to specific surface areas as high as 153-284m2g-1. Aerogels based on different NFC nanofibers were studied by FE-SEM, BET analysis (nitrogen gas adsorption), and mechanical properties were measured in compression for different densities of aerogels. The properties are compared with polymer foams and inorganic aerogels. Compared with cellular NFC foams, the present nanofibrous aerogels have lower modulus and show lower stress in compression for a given strain. Tert-butanol freeze-drying can therefore be used to create " soft" aerogels. © 2011 Elsevier Ltd.


Alvehag K.,KTH Royal Institute of Technology | Soder L.,KTH Royal Institute of Technology
IET Generation, Transmission and Distribution | Year: 2011

In the re-regulated electricity market, there is a growing interest in performance-based regulation accompanied by quality regulation for electric distribution networks. This study develops a new risk-based method for reliability investment decisions when the distribution system operator (DSO) is exposed to financial risks defined by a quality regulation. As quality regulation design becomes more complex, more detailed risk management methods are needed in order to adequately capture the financial risk the DSO is exposed to. The proposed method applies the Monte-Carlo simulation technique in order to assess the risks of the considered reinvestment projects. By using the proposed method, the impacts that different risk strategies (risk-neutral/risk-averse) and risk models (non-time-varying/time-varying) have on which reinvestment project is selected is investigated in a case study. This is investigated for two different quality regulation designs. The results show that primarily not only the quality regulation design but also the risk model formulation and risk strategy have a major impact on which reinvestment project is selected. © 2011 The Institution of Engineering and Technology.


Kroon M.,KTH Royal Institute of Technology
Engineering Fracture Mechanics | Year: 2011

Asymptotic analyses of the mechanical fields in front of stationary and propagating cracks are important for several reasons. For example, they facilitate the understanding of the mechanical and physical state in front of crack tips, and they enable prediction of crack growth. Furthermore, efficient modelling of arbitrary crack growth by use of XFEM (extended finite element method) requires accurate knowledge of the asymptotic crack tip fields. The present study focuses on the asymptotic fields in front of a crack that propagates dynamically in rubber. Static analyses of this type of problem have been made in previous studies. In order to be able to compare the present results with these earlier studies, the constitutive model from Knowles and Sternberg (J. Elast. 3:67-107, 1973) was adopted. It is assumed that viscoelastic stresses become negligible compared with the singular elastic stresses close to the crack tip. The present analysis shows that in materials with a significant hardening, the inertia term in the equations of motion becomes negligible in the asymptotic analysis. However, for a neoHookean type of model, inertia comes into play and causes a maximum theoretical crack speed that equals the shear wave speed. © 2011 Elsevier Ltd.


Eriksson R.,KTH Royal Institute of Technology | Soder L.,KTH Royal Institute of Technology
IEEE Transactions on Power Delivery | Year: 2011

The contribution of this paper is the application of subspace system identification techniques, to derive a low-order black-box state-space model of a power system with many controllable devices using global signals. This model is a multiinput, multioutput open system model describing the power oscillatory behavior of the power system. The input signals are the controllable setpoints of the controllable devices, the output signals are the speed of selected generators measured by a wide-area measurement system. This paper describes how to achieve and preprocess the data to use subspace techniques to estimate and validate to finally assign an accurate model. This new approach can be used directly to design a central coordinating controller for all of the relevant controllable devices, with the aim to increase the damping of the modes in the system. Previously presented methods use local measurements or output signals dependent on the actual operational point. The benefit of the presented method is that the used output signals are independent of the system state. This makes it possible to use state-feedback control to combine the controllable devices to coordinately damp the modes. The presented method is applied in the CIGR Nordic 32-bus system including two HVDC links. The case study demonstrates that accurate low-order state-space models can be estimated and validated by using the described method to accurately model the system's power oscillatory behavior. © 2011 IEEE.


Niu X.,KTH Royal Institute of Technology | Ban Y.,KTH Royal Institute of Technology
International Journal of Remote Sensing | Year: 2013

We have investigated multi-temporal polarimetric synthetic aperture radar (SAR) data for urban land-cover classification using an object-based support vector machine (SVM) in combinations of rules. Six-date RADARSAT-2 high-resolution polarimetric SAR data in both ascending and descending passes were acquired in the rural-urban fringe of the Greater Toronto Area during the summer of 2008. The major land-use/land-cover classes include high-density residential areas, low-density residential areas, industrial and commercial areas, construction sites, parks, golf courses, forests, pasture, water, and two types of agricultural crops. Various polarimetric SAR parameters were evaluated for urban land-cover mapping and they include the parameters from Pauli, Freeman and Cloude-Pottier decompositions, the coherency matrix, intensities of each polarization, and their logarithm forms. The multi-temporal SAR polarimetric features were classified first using an SVM classifier. Then specific rules were developed to improve the SVM classification results by extracting major roads and streets using shape features and contextual information. For the comparison of the polarimetric SAR parameters, the best classification performance was achieved using the compressed logarithmic filtered Pauli parameters. For the evaluation of the multi-temporal SAR data set, the best classification result was achieved using all six-date data (kappa = 0.91), while very good classification results (kappa = 0.86) were achieved using only three-date polarimetric SAR data. The results indicate that the combination of both the ascending and the descending polarimetric SAR data with an appropriate temporal span is suitable for urban land-cover mapping. © 2012 Taylor & Francis.


Skog I.,KTH Royal Institute of Technology | Handel P.,KTH Royal Institute of Technology
IEEE Transactions on Signal Processing | Year: 2010

Accurate clock synchronization is vital to many applications of wireless sensor networks (WSNs). The availability of a mathematical tool that at an early design stage can provide insight into the theoretically achievable performance of the clock synchronization may accordingly be valuable in the initial design phase of the network. Therefore, the achievable clock synchronization accuracy is examined in a WSN employing a two-way message exchange model under a Gaussian assumption. The Cramr-Rao bound for the estimation of the clock parameters is derived for four different parameterizations (i.e., different nuisance parameters), reflecting different levels of prior knowledge concerning the system parameters. The results on the Cramér-Rao bound are transformed into a lower bound on the mean square error of the clock offset, a figure of merit often more relevant, characterizing the system performance. Further, by introducing a set of artificial observations through a linear combination of the observations originally obtained in the two-way message exchange, an approximate maximum likelihood estimator for the clock parameters is proposed. The estimator is shown to be of low complexity and it obeys near-optimal performance, that is, a mean square error in the vicinity of the Cramé-Rao bound. The applicability of the derived results is shown through a simulation study of an offshore engineering scenario, where a remotely operated underwater vehicle is used for operations at the seabed. The position of the vehicle is tracked using a WSN. © 2006 IEEE.


Bjornson E.,KTH Royal Institute of Technology | Ottersten B.,KTH Royal Institute of Technology | Ottersten B.,University of Luxembourg
IEEE Transactions on Signal Processing | Year: 2010

In this paper, we create a framework for trainingbased channel estimation under different channel and interference statistics. The minimum mean square error (MMSE) estimator for channel matrix estimation in Rician fading multi-antenna systems is analyzed, and especially the design of mean square error (MSE) minimizing training sequences. By considering Kronecker-structured systems with a combination of noise and interference and arbitrary training sequence length, we collect and generalize several previous results in the framework. We clarify the conditions for achieving the optimal training sequence structure and show when the spatial training power allocation can be solved explicitly. We also prove that spatial correlation improves the estimation performance and establish how it determines the optimal training sequence length. The analytic results for Kronecker-structured systems are used to derive a heuristic training sequence under general unstructured statistics. The MMSE estimator of the squared Frobenius norm of the channel matrix is also derived and shown to provide far better gain estimates than other approaches. It is shown under which conditions training sequences that minimize the non-convex MSE can be derived explicitly or with low complexity. Numerical examples are used to evaluate the performance of the two estimators for different training sequences and system statistics. We also illustrate how the optimal length of the training sequence often can be shorter than the number of transmit antennas. © 2010 IEEE.


Edlund U.,KTH Royal Institute of Technology | Albertsson A.-C.,KTH Royal Institute of Technology
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2012

Robust and versatile controlled radical polymerization, also in air, was achieved via single electron transfer living radical polymerization (SET-LRP) initiated by purposely designed hemicellulose-derived macroinitiators. The efficiency of the substitution reaction, converting the polysaccharides into bromo-multifunctionalized initiators, as well as the rate of subsequent induced polymerizations of methyl acrylate were controlled by the hemicellulose repeating unit structure, branching pattern, and molecular weight. Macroinitiators with mannan-based backbones induce SET-LRP with somewhat higher apparent rate constants than xylan-derived analogues, increasing by a factor two to three when raising the reaction temperature from 25 to 40 °C. The presence of lignin in a nonpurified xylan fraction did not impair its viability as a macroinitiator. Hemicellulose-initiated SET-LRP was feasible in air, proceeding with comparable or somewhat higher apparent rate constants than when conducted under deoxygenated conditions. © 2012 Wiley Periodicals, Inc.


Fransen E.,KTH Royal Institute of Technology
Progress in molecular biology and translational science | Year: 2014

Chronic pain constitutes an important and growing problem in society with large unmet needs with respect to treatment and clear implications for quality of life. Computational modeling is used to complement experimental studies to elucidate mechanisms involved in pain states. Models representing the peripheral nerve ending often address questions related to sensitization or reduction in pain detection threshold. In models of the axon or the cell body of the unmyelinated C-fiber, a large body of work concerns the role of particular sodium channels and mutations of these. Furthermore, in central structures: spinal cord or higher structures, sensitization often refers not only to enhanced synaptic efficacy but also to elevated intrinsic neuronal excitability. One of the recent developments in computational neuroscience is the emergence of computational neuropharmacology. In this area, computational modeling is used to study mechanisms of pathology with the objective of finding the means of restoring healthy function. This research has received increased attention from the pharmaceutical industry as ion channels have gained increased interest as drug targets. Computational modeling has several advantages, notably the ability to provide mechanistic links between molecular and cellular levels on the one hand and functions at the systems level on the other hand. These characteristics make computational modeling an additional tool to be used in the process of selecting pharmaceutical targets. Furthermore, large-scale simulations can provide a framework to systematically study the effects of several interacting disease parameters or effects from combinations of drugs. © 2014 Elsevier Inc. All rights reserved.


Forsell C.,KTH Royal Institute of Technology | Gasser T.C.,KTH Royal Institute of Technology
Journal of Biomechanics | Year: 2011

Lead perforation is a rare but serious clinical complication of pacemaker implantation, and towards understanding this malfunction, the present study investigated myocardial failure due to deep penetration by an advancing rigid punch. To this end, a non-linear Finite Element model was developed that integrates constitutive data published in the literature with information from in vitro tensile testing in cross-fibre direction of porcine myocardial tissue. The Finite Element model considered non-linear, isotropic and visco-elastic properties of the myocardium, and tissue failure was phenomenologically described by a Traction Separation Law. In vitro penetration testing of porcine myocardium was used to validate the Finite Element model, and a particular objective of the study was to investigate the impact of different constitutive parameters on the simulated results. Specifically, results demonstrated that visco-elastic properties of the tissue strongly determine the failure process, whereas dissipative effects directly related to failure had a minor impact on the simulation results. In addition, non-linearity of the bulk material did not change the predicted peak penetration force and the simulations did not reveal elastic crack-tip blunting. The performed study provided novel insights into ventricular failure due to deep penetration, and provided useful information with which to develop numerical failure models. © 2010 Elsevier Ltd.


Sjoberg L.E.,KTH Royal Institute of Technology
Geophysical Journal International | Year: 2013

In this study,we showthat the traditionally defined Bouguer gravity anomaly needs a correction to become 'the no-topography gravity anomaly' and that the isostatic gravity anomaly is better defined by the latter anomaly plus a gravity anomaly compensation effect than by the Bouguer gravity anomaly plus a gravitational compensation effect. This is because only the newisostatic gravity anomaly completely removes and compensates for the topographic effect. F. A. Vening Meinesz' inverse problem in isostasy deals with solving for the Moho depth from the known external gravity field and mean Moho depth (known, e.g. from seismic reflection data) by a regional isostatic compensation using a flat Earth approximation. H. Moritz generalized the problem to that of a global compensation with a spherical mean Earth approximation. The problem can be formulated mathematically as that of solving a non-linear Fredholm integral equation. The solutions to these problems are based on the condition of isostatic balance of the isostatic gravity anomaly, and, theoretically, this assumption cannot be met by the old definition of the isostatic gravity anomaly. We show how the Moho geometry can be solved for the gravity anomaly, gravity disturbance and disturbing potential, etc., and, from a theoretical point of view, all these solutions are the same. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.


Yousif O.,KTH Royal Institute of Technology | Ban Y.,KTH Royal Institute of Technology
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

Multitemporal synthetic aperture radar (SAR) images have been increasingly used in change detection studies. However, the presence of speckle is the main disadvantage of this type of data. To reduce speckle, many local adaptive filters have been developed. Although these filters are effective in reducing speckle in homogeneous areas, their use is often accompanied with the degradation of spatial details and fine structures. In this paper, we investigate a nonlocal means (NLM) denoising algorithm that combines local structures with a global averaging scheme in the context of change detection using multitemporal SAR images. First, the ratio image is logarithmically scaled to convert the multiplicative noise model to an additive model. A multidimensional change image is then constructed using image neighborhood feature vectors. Principle component analysis is then used to reduce the dimensionality of the neighborhood feature vectors. Recursive linear regression combined with fitting-accuracy assessment strategy is developed to determine the number of significant PC components to be retained for similarity weight computation. An intuitive method to estimate the unknown noise variance (necessary to run the NLM algorithm) based on the discarded PC components is also proposed. The efficiency of the method has been assessed using two different bitemporal SAR datasets acquired in Beijing and Shanghai, respectively. For comparison purposes, the algorithm is also tested against some of the most commonly used local adaptive filters. Qualitative and quantitative analyses of the algorithm have demonstrated the efficiency of the algorithm in recovering the noise-free change image while preserving the complex structures in urban areas. © 1980-2012 IEEE.


Augier P.,KTH Royal Institute of Technology | Lindborg E.,KTH Royal Institute of Technology
Journal of the Atmospheric Sciences | Year: 2013

A new formulation of the spectral energy budget of kinetic and available potential energies of the atmosphere is derived, with spherical harmonics as base functions. Compared to previous formulations, there are three main improvements: (i) the topography is taken into account, (ii) the exact three-dimensional advection terms are considered, and (iii) the vertical flux is separated from the energy transfer between different spherical harmonics. Using this formulation, results from two different high-resolution GCMs are analyzed: the Atmospheric GCM for the Earth Simulator (AFES) T639L24 and the European Centre for Medium- Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS) T1279L91. The spectral fluxes show that the AFES, which reproduces quite realistic horizontal spectra with a k-5/3 inertial range at the mesoscales, simulates a strong downscale energy cascade. In contrast, neither the k-5/3 vertically integrated spectra nor the downscale energy cascade are produced by the ECMWF IFS. © 2013 American Meteorological Society.


Eshagh M.,KTH Royal Institute of Technology
Acta Geodaetica et Geophysica | Year: 2013

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission is dedicated to recover spherical harmonic coefficients of the Earth's gravity field to degree and order of about 250 using its satellite gradiometric data. Since these data are contaminated with coloured noise, therefore, their inversion will not be straightforward. Unsuccessful modelling of this noise will lead to biases in the harmonic coefficients presented in the Earth's gravity models (EGMs). In this study, five of the recent EGMs of GOCE such as two direct, two time-wise and one space-wise solution are used to degree and order 240 and their reliability is investigated with respect to EGM08 which is assumed as a reliable EGM. The detected unreliable coefficients and their errors are replaced by the corresponding ones from EGM08 as a combination strategy. A condition adjustment model is organised for each two corresponding coefficients of GOCE EGMs and EGM08; and errors of the GOCE EGMs are calibrated based on a scaling factor, obtained from a posteriori variance factor. When the factor is less than 2.5 it will be multiplied to the error otherwise the error of EGM08 coefficient will be considered as the calibrated one. At the end, a simple geoid estimator is presented which considers the EGMs and their errors and its outcomes are compared with the corresponding geoid heights derived from the Global Positioning System (GPS) and the levelling data (GPS/levelling data), over Fennoscandia. This comparison shows that some of the combined-calibrated GOCE EGMs are closer to the GPS/levelling data than the original ones. © 2013 Akadémiai Kiadó, Budapest, Hungary.


Du G.,KTH Royal Institute of Technology | Karoumi R.,KTH Royal Institute of Technology
Structure and Infrastructure Engineering | Year: 2013

Railway bridges currently encounter the challenges of increasing the load capacity while the environmental sustainability should be achieved. However, it has been realised that the environmental assessment of railway bridges has not been integrated into the decision-making process, the standard guideline and criterion is still missing in this field. Therefore, the implementation of life cycle assessment (LCA) method is introduced into railway bridges. This article provides a systematic bridge LCA model as a guideline to quantify the environmental burdens for the railway bridge structures. A comparison case study between two alternative designs of Banafjäl Bridge is further carried out through the whole life cycle, with the consideration of several key maintenance and end-of-life scenarios. Six impact categories are investigated by using the LCA CML 2001 method and the known life cycle inventory database. Results show that the fixed-slab bridge option has a better environmental performance than the ballasted design due to the ease of maintenances. The initial material manufacture stage is responsible for the largest environmental burden, while the impacts from the construction machinery and material transportations are ignorable. Sensitivity analysis illustrates the maintenance scenario planning and steel recycling have the significant influence on the final results other than the traffic disturbances. © 2013 Copyright Taylor and Francis Group, LLC.


Al-Naqshabandy M.S.,KTH Royal Institute of Technology | Larsson S.,KTH Royal Institute of Technology
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

The strength variability of soils improved by lime-cement columns is very high, and assessment of the reliability is associated with high uncertainty. Previous research on natural soils has shown that variability has a major impact on the reliability of geotechnical systems. However, concerning ground improvement with lime-cement columns, the effect of the uncertainties associated with improved strength properties on the reliability isunknown. This paper addresses the integration of reliability-based design in the design of embankments founded on soil improved by lime-cement columns by an analysis of a project conducted in Sweden. The uncertainties associated with estimating the strength property based on results from cone penetration tests and their effect on the assessed system reliability are addressed and discussed. The use of variance reduction with respect to the spatial variability of the shear strength of the columns was found to have a major influence on the assessed system reliability. Furthermore, it was found that the transformation uncertainty from measurements based on cone penetration tests has a significant impact on the assessed system reliability. System reliability cannot be improved significantly simply by performing a large number of tests. © 2013 American Society of Civil Engineers.


Wilde M.W.,AF Industry AB | Johansson F.,KTH Royal Institute of Technology
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

Structural reliability analysis is not widely used for the design and assessment of concrete dams. In this paper, the system reliability of a spillway structure consisting of two monoliths is calculated. Limit state functions are defined from the failure modes sliding in the concrete rock contact, sliding in the rock mass, and adjusted overturning. Random variables in the limit state functions are defined by stochastic distributions. These are defined based on site investigations and laboratory tests from samples taken at the dam. Simulations and information from the literature are used for the remaining variables. The safety index is calculated by the first-order reliability method for each failure mode and monolith, and the system reliability is approximated by direct integration of the bivariate normal distribution. The output is the safety index including associated sensitivity values at the single failure mode, monolith, and system levels. The results show that the system safety is governed by a persistent rock joint beneath one monolith. A system reliability analysis is found to be a useful tool in the dam risk management process as it can be used to calculate the probability of failure and to identify important failure modes and variables. © 2013 American Society of Civil Engineers.


Schenk L.,KTH Royal Institute of Technology
International Journal of Occupational and Environmental Health | Year: 2010

It has previously been shown that occupational exposure limits (OELs) for the same substance can vary significantly between different standard-setters. The work presented in this paper identifies the steps in the process towards establishing an OEL and how variations in those processes could account for these differences. This study selects for further scrutiny substances for which the level of OELs vary by a factor of 100, focussing on 45 documents concerning 14 substances from eight standard-setters. Several of the OELs studied were more than 20 years old and based on outdated knowledge. Furthermore, different standard-setters sometimes based their OELs on different sets of data, and data availability alone could not explain all differences in the selection of data sets used by standard-setters. While the interpretation of key studies did not differ significantly in standard-setters' documentations, the evaluations of the key studies' quality did. Also, differences concerning the critical effect coincided with differences in the level of OELs for half of the substances.


Martufi G.,KTH Royal Institute of Technology | Gasser T.C.,KTH Royal Institute of Technology
Journal of Biomechanics | Year: 2011

A fundamental understanding of the mechanical properties of the extracellular matrix (ECM) is critically important to quantify the amount of macroscopic stress and/or strain transmitted to the cellular level of vascular tissue. Structural constitutive models integrate histological and mechanical information, and hence, allocate stress and strain to the different microstructural components of the vascular wall. The present work proposes a novel multi-scale structural constitutive model of passive vascular tissue, where collagen fibers are assembled by proteoglycan (PG) cross-linked collagen fibrils and reinforce an otherwise isotropic matrix material. Multiplicative kinematics account for the straightening and stretching of collagen fibrils, and an orientation density function captures the spatial organization of collagen fibers in the tissue. Mechanical and structural assumptions at the collagen fibril level define a piece-wise analytical stress-stretch response of collagen fibers, which in turn is integrated over the unit sphere to constitute the tissue's macroscopic mechanical properties. The proposed model displays the salient macroscopic features of vascular tissue, and employs the material and structural parameters of clear physical meaning. Likewise, the constitutive concept renders a highly efficient multi-scale structural approach that allows for the numerical analysis at the organ level. Model parameters were estimated from isotropic mean-population data of the normal and aneurysmatic aortic wall and used to predict in-vivo stress states of patient-specific vascular geometries, thought to demonstrate the robustness of the particular Finite Element (FE) implementation. The collagen fibril level of the multi-scale constitutive formulation provided an interface to integrate vascular wall biology and to account for collagen turnover. © 2011 Elsevier Ltd.


Holm H.,KTH Royal Institute of Technology
Proceedings of the Annual Hawaii International Conference on System Sciences | Year: 2014

A frequent claim that has not been validated is that signature based network intrusion detection systems (SNIDS) cannot detect zero-day attacks. This paper studies this property by testing 356 severe attacks on the SNIDS Snort, configured with an old official rule set. Of these attacks, 183 attacks are zero-days' to the rule set and 173 attacks are theoretically known to it. The results from the study show that Snort clearly is able to detect zero-days' (a mean of 17% detection). The detection rate is however on overall greater for theoretically known attacks (a mean of 54% detection). The paper then investigates how the zero-days' are detected, how prone the corresponding signatures are to false alarms, and how easily they can be evaded. Analyses of these aspects suggest that a conservative estimate on zero-day detection by Snort is 8.2%. © 2014 IEEE.


Gattami A.,Massachusetts Institute of Technology | Gattami A.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2010

We consider the problem of stochastic finite- and infinite-horizon linear quadratic control under power constraints. The calculations of the optimal control law can be done off-line as in the classical linear quadratic Gaussian control theory using dynamic programming, which turns out to be a special case of the new theory developed in this technical note. A numerical example is solved using the new methods. © 2009 IEEE.


Ban Y.,KTH Royal Institute of Technology | Jacob A.,KTH Royal Institute of Technology
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

The objectives of this research are to develop robust methods for segmentation of multitemporal synthetic aperture radar (SAR) and optical data and to investigate the fusion of multitemporal ENVISAT advanced synthetic aperture radar (ASAR) and Chinese HJ-1B multispectral data for detailed urban land-cover mapping. Eight-date multiangle ENVISAT ASAR images and one-date HJ-1B charge-coupled device image acquired over Beijing in 2009 are selected for this research. The edge-aware region growing and merging (EARGM) algorithm is developed for segmentation of SAR and optical data. Edge detection using a Sobel filter is applied on SAR and optical data individually, and a majority voting approach is used to integrate all edge images. The edges are then used in a segmentation process to ensure that segments do not grow over edges. The segmentation is influenced by minimum and maximum segment sizes as well as the two homogeneity criteria, namely, a measure of color and a measure of texture. The classification is performed using support vector machines. The results show that our EARGM algorithm produces better segmentation than eCognition, particularly for built-up classes and linear features. The best classification result (80%) is achieved using the fusion of eight-date ENVISAT ASAR and HJ-1B data. This represents 5%, 11%, and 14% improvements over eCognition, HJ-1B, and ASAR classifications, respectively. The second best classification is achieved using fusion of four-date ENVISAT ASAR and HJ-1B data (78%). The result indicates that fewer multitemporal SAR images can achieve similar classification accuracy if multitemporal multiangle dual-look-direction SAR data are carefully selected. © 1980-2012 IEEE.


Radon, radium and helium data from three sites in granitic rock in Sweden (Forsmark and Laxemar) and Finland (Olkiluoto) from depths greater than 1,000 m were interpreted by a model that describes how daughter nuclides, including helium from uranium and thorium decay, escape from minerals, enter the pore water in the rock matrix and diffuse to the seeping water in the fractures in the rock. The radium concentrations are on the order of <30 Bq/l of water that has recently infiltrated and then emerged from the rock. Radon concentrations are mostly several orders of magnitude larger. The model predicts values in the same range. The fair agreement between model results, field data and laboratory data over a scale spanning micrometres over meters to kilometres, and time scales of days to millions of years, shows that the micropores of the rock matrix are connected even at depths down to and beyond a kilometre. Molecular diffusion in the matrix pore water is a key migration mechanism. Laboratory-derived sorption coefficients for radium are of the same magnitude as those needed in the modelling of the in situ data to give good agreement. © 2013 Springer-Verlag Berlin Heidelberg.


Gudnason S.B.,CAS Lanzhou Institute of Modern Physics | Gudnason S.B.,KTH Royal Institute of Technology | Nitta M.,Keio University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We study a Skyrme-type model with a quadratic potential for a field with S2 vacua. We consider two flavors of the model, the first is the Skyrme model and the second has a sixth-order derivative term instead of the Skyrme term; both with the added quadratic potential. The model contains molecules of half Skyrmions, each of them is a global (anti)monopole with baryon number 1/2. We numerically construct solutions with baryon numbers one through six, and find stable solutions which look like beads on rings. We also construct a molecule with fractional Skyrmions having the baryon numbers 1/3+2/3, by adding a linear potential term. © 2015 American Physical Society.


Toll S.,KTH Royal Institute of Technology
Acta Mechanica | Year: 2011

Standard hypoplasticity is examined with respect to the thermodynamic requirement of non-negative energy dissipation. We introduce a stress energy function and derive a dissipation inequality in terms of the stress-dependent operators of the hypoplastic law. A general form for the non-linear operator is also found, which makes it straightforward to construct thermodynamically consistent hypoplasticity laws. We further examine the subclass of hypoplasticity where the linear term is non-dissipative and construct some examples of hypoplastic laws based on a quadratic stress energy function. © 2011 The Author(s).


Endalew A.K.,KTH Royal Institute of Technology | Kiros Y.,KTH Royal Institute of Technology | Zanzi R.,KTH Royal Institute of Technology
Energy | Year: 2011

This work focuses on the development of heterogeneous catalysts for biodiesel production from high free fatty acid (FFA) containing Jatropha curcas oil (JCO). Solid base and acid catalysts were prepared and tested for transesterification in a batch reactor under mild reaction conditions. Mixtures of solid base and acid catalysts were also tested for single-step simultaneous esterification and transesterification. More soap formation was found to be the main problem for calcium oxide (CaO) and lithium doped calcium oxide (Li-CaO) catalysts during the reaction of jatropha oil and methanol than for the rapeseed oil (RSO). CaO with Li doping showed increased conversion to biodiesel than bare CaO as a catalyst. La2O3/ZnO, La2O3/Al2O3 and La0.1Ca0.9MnO3 catalysts were also tested and among them La2O3-ZnO showed higher activity. Mixture of solid base catalysts (CaO and Li-CaO) and solid acid catalyst (Fe2(SO4)3) were found to give complete conversion to biodiesel in a single-step simultaneous esterification and transesterification process. © 2011 Elsevier Ltd.


Mainali B.,KTH Royal Institute of Technology | Silveira S.,KTH Royal Institute of Technology
Energy | Year: 2011

More than 61% of the total population of Nepal has no access to electricity. The majority is poor and live in rural areas. In recent years, rural electrification has had high priority in government policies, and micro hydro and solar PV have been the most commonly adopted off-grid technologies. The financial mix in the off-grid rural electrification is generally characterized by subsidy, equity and credit. In this paper, we analyze how rural electrification has been funded and the impact of subsidy policies on the renewable energy market, focusing on the projects implemented under the 'subsidy policy 2000'. Our study is based on official data obtained from authorities in Nepal and a survey carried out among private supply and installation companies, NGOs and financial institutions. The study shows that awareness levels in adopting RE-technologies and willingness of people to access and pay for electricity have increased significantly. However, there is a huge financial gap between the cost of electrification and the affordability. Bridging this gap is a crucial issue that needs to be addressed for the smooth expansion of rural electrification in the country. © 2010 Elsevier Ltd.


Levenius M.,KTH Royal Institute of Technology | Pasiskevicius V.,KTH Royal Institute of Technology | Gallo K.,KTH Royal Institute of Technology
Applied Physics Letters | Year: 2012

We investigate the effect of angular tuning on coherently coupled optical parametric generation (OPG) in two-dimensional purely nonlinear lattices and demonstrate how it allows accessing both shared signal and shared idler regimes, resulting in twin-beam outputs in the mid- and near infrared, respectively. Furthermore, we present the results of a systematic spectral and angular mapping of the twin-beam OPG response in the near-infrared as a function of the pump incidence angle. © 2012 American Institute of Physics.


Ostling M.,KTH Royal Institute of Technology
Science China Information Sciences | Year: 2011

Silicon carbide (SiC) semiconductor devices for high power applications are now commercially available as discrete devices. Recently Schottky diodes are offered by both USA and Europe based companies. Active switching devices such as bipolar junction transistors (BJTs), field effect transistors (JFETs and MOSFETs) are now reaching the market. The interest is rapidly growing for these devices in high power and high temperature applications. The main advantages of wide bandgap semiconductors are their very high critical electric field capability. From a power device perspective the high critical field strength can be used to design switching devices with much lower losses than conventional silicon based devices both for on-state losses and reduced switching losses. This paper will review the current state of the art in active switching device performance for both SiC and GaN devices. SiC material quality and epitaxy processes have greatly improved and degradation free 100 mm wafers are readily available. This is encouraging since also bipolar devices now are attractive with good long term stability. SiC wafers still have a too high cost to be fully cost efficient. However, the SiC wafer roadmap looks very favorable as volume production takes off. For GaN materials the main application area is geared towards the lower power rating level up to 1 kV on mostly lateral FET designs. The cost advantage is interesting for GaN when grown on Si substrates to bring down costs. © Science China Press and Springer-Verlag Berlin Heidelberg 2011.


Lundqvist M.,KTH Royal Institute of Technology
PLoS computational biology | Year: 2010

Attractor neural networks are thought to underlie working memory functions in the cerebral cortex. Several such models have been proposed that successfully reproduce firing properties of neurons recorded from monkeys performing working memory tasks. However, the regular temporal structure of spike trains in these models is often incompatible with experimental data. Here, we show that the in vivo observations of bistable activity with irregular firing at the single cell level can be achieved in a large-scale network model with a modular structure in terms of several connected hypercolumns. Despite high irregularity of individual spike trains, the model shows population oscillations in the beta and gamma band in ground and active states, respectively. Irregular firing typically emerges in a high-conductance regime of balanced excitation and inhibition. Population oscillations can produce such a regime, but in previous models only a non-coding ground state was oscillatory. Due to the modular structure of our network, the oscillatory and irregular firing was maintained also in the active state without fine-tuning. Our model provides a novel mechanistic view of how irregular firing emerges in cortical populations as they go from beta to gamma oscillations during memory retrieval.


Gudnason S.B.,KTH Royal Institute of Technology | Nitta M.,Keio University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We study a Skyrme-type model with a potential term motivated by Bose-Einstein condensates (BECs), which we call the BEC Skyrme model. We consider two flavors of the model: the first is the Skyrme model, and the second has a sixth-order derivative term instead of the Skyrme term, both with the added BEC-motivated potential. The model contains toroidally shaped Skyrmions, and they are characterized by two integers P and Q, representing the winding numbers of two complex scalar fields along the toroidal and poloidal cycles of the torus, respectively. The baryon number is B=PQ. We find stable Skyrmion solutions for P=1,2,3,4,5 with Q=1, while for P=6 and Q=1, it is only metastable. We further find that configurations with higher Q>1 are all unstable and split into Q configurations with Q=1. Finally we discover a phase transition, possibly of first order, in the mass parameter of the potential under study. © 2015 American Physical Society.


Humble M.S.,KTH Royal Institute of Technology | Berglund P.,KTH Royal Institute of Technology
European Journal of Organic Chemistry | Year: 2011

Enzymes are attractive catalysts because of their promiscuity and their ability to perform highly regio-, chemo- and stereoselective transformations. Enzyme promiscuity allows optimisation of industrial processes that require reaction conditions different from those in nature. Many enzymes can be used in reactions completely different from the reaction the enzyme originally evolved to perform. Such catalytically promiscuous reactions can be secondary activities hidden behind a native activity and might be discovered either in screening for that particular activity or, alternatively, by chance. Recently, researchers have designed enzymes to show catalytic promiscuity. It is also possible to design new enzymes from scratch by computer modelling (de novo design), but most work published to date starts from a known enzyme backbone. Promiscuous activity might also be induced or enhanced by rational design or directed evolution (or combinations thereof). Enzyme catalytic promiscuity provides fundamental knowledge about enzyme/substrate interactions and the evolution of new enzymes. New enzymes are required by industry, which needs to optimise chemical processes in an environmentally sustainable way. In this review various aspects of enzyme catalytic promiscuity are considered from a biocatalytic perspective. Enzyme catalytic promiscuity, which can allow application of enzymes for non-natural reactions, is a recently recognised frontier in biocatalysis. This behaviour can be found in nature in the form of a secondary activity of an enzyme or can be developed by protein engineering. Recent examples that might provide new tools for synthetic chemists are considered from a biocatalytic perspective. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Cvetkovic V.,KTH Royal Institute of Technology
Environmental Research Letters | Year: 2011

A generalized distribution for the water residence time in hydrological transport is proposed in the form of the tempered one-sided stable (TOSS) density. It is shown that limiting cases of the TOSS distribution recover virtually all distributions that have been considered in the literature for hydrological transport, from plug flow to flow reactor, the advection-dispersion model, and the gamma and Levy densities. The stable property of TOSS is particularly important, enabling a seamless transition between a time-domain random walk, and the Lagrangian (trajectory) approach along hydrological transport pathways. © 2011 IOP Publishing Ltd.


Pacini H.,KTH Royal Institute of Technology | Silveira S.,KTH Royal Institute of Technology
Energy Policy | Year: 2011

The introduction of flex-fuel vehicles since 2003 has made possible for Brazilian drivers to choose between high ethanol blends or gasoline depending on relative prices and fuel economies. In Sweden, flex-fuel fleets were introduced in 2005. Prices and demand data were examined for both Brazil and Sweden. Bioethanol has been generally the most cost-efficient fuel in Brazil, but not for all states. In any case, consumers in Brazil have opted for ethanol even when this was not the optimal economic choice. In Sweden, a different behavior was observed when falling gasoline prices made E85 uneconomical in late 2008. In a context of international biofuels expansion, the example of E85 in Sweden indicates that new markets could experience different consumer behavior than Brazil: demand falls rapidly with reduced price differences between ethanol and gasoline. At the same time, rising ethanol demand and lack of an international market with multiple biofuel producers could lead to higher domestic prices in Brazil. Once the limit curve is crossed, the consumer might react by shifting back to the usage of gasoline. © 2010 Elsevier Ltd.


Gudnason S.B.,KTH Royal Institute of Technology | Nitta M.,Keio University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We construct a D-brane soliton, a composite topological soliton sharing some properties with a D-brane, in a Skyrme model in 4+1 dimensions, in which Skyrmions are strings ending on a domain wall. We further generalize this D-brane soliton to diverse dimensions. A string, carrying the πN-1 topological charge, ends on a domain wall in an O(N) model with higher-derivative terms in N+1 dimensions. © 2015 American Physical Society.


Endalew A.K.,KTH Royal Institute of Technology | Kiros Y.,KTH Royal Institute of Technology | Zanzi R.,KTH Royal Institute of Technology
Biomass and Bioenergy | Year: 2011

Biofuels are renewable solutions to replace the ever dwindling energy reserves and environmentally pollutant fossil liquid fuels when they are produced from low cost sustainable feedstocks. Biodiesel is mainly produced from vegetable oils or animal fats by the method of transesterification reaction using catalysts. Homogeneous catalysts are conventionally used for biodiesel production. Unfortunately, homogeneous catalysts are associated with problems which might increase the cost of production due to separation steps and emission of waste water. Inorganic heterogeneous catalysts are potentially low cost and can solve many of the problems encountered in homogeneous catalysts. Many solid acid and base inorganic catalysts have been studied for the transesterification of various vegetables oils. The work of many researchers on the development of active, tolerant to water and free fatty acids (FFA), as well as stable inorganic catalysts for biodiesel production from vegetable oils are reviewed and discussed. © 2011 Elsevier Ltd.


Gliga A.R.,Karolinska Institutet | Skoglund S.,KTH Royal Institute of Technology | Odnevall Wallinder I.,KTH Royal Institute of Technology | Fadeel B.,Karolinska Institutet | Karlsson H.L.,Karolinska Institutet
Particle and Fibre Toxicology | Year: 2014

Background: Silver nanoparticles (AgNPs) are currently one of the most manufactured nanomaterials. A wide range of toxicity studies have been performed on various AgNPs, but these studies report a high variation in toxicity and often lack proper particle characterization. The aim of this study was to investigate size- and coating-dependent toxicity of thoroughly characterized AgNPs following exposure of human lung cells and to explore the mechanisms of toxicity.Methods: BEAS-2B cells were exposed to citrate coated AgNPs of different primary particle sizes (10, 40 and 75 nm) as well as to 10 nm PVP coated and 50 nm uncoated AgNPs. The particle agglomeration in cell medium was investigated by photon cross correlation spectroscopy (PCCS); cell viability by LDH and Alamar Blue assay; ROS induction by DCFH-DA assay; genotoxicity by alkaline comet assay and γH2AX foci formation; uptake and intracellular localization by transmission electron microscopy (TEM); and cellular dose as well as Ag release by atomic absorption spectroscopy (AAS).Results: The results showed cytotoxicity only of the 10 nm particles independent of surface coating. In contrast, all AgNPs tested caused an increase in overall DNA damage after 24 h assessed by the comet assay, suggesting independent mechanisms for cytotoxicity and DNA damage. However, there was no γH2AX foci formation and no increased production of intracellular reactive oxygen species (ROS). The reasons for the higher toxicity of the 10 nm particles were explored by investigating particle agglomeration in cell medium, cellular uptake, intracellular localization and Ag release. Despite different agglomeration patterns, there was no evident difference in the uptake or intracellular localization of the citrate and PVP coated AgNPs. However, the 10 nm particles released significantly more Ag compared with all other AgNPs (approx. 24 wt% vs. 4-7 wt%) following 24 h in cell medium. The released fraction in cell medium did not induce any cytotoxicity, thus implying that intracellular Ag release was responsible for the toxicity.Conclusions: This study shows that small AgNPs (10 nm) are cytotoxic for human lung cells and that the toxicity observed is associated with the rate of intracellular Ag release, a 'Trojan horse' effect. © 2014 Gliga et al.; licensee BioMed Central Ltd.


Biasetti J.,KTH Royal Institute of Technology | Hussain F.,University of Houston | Christian Gasser T.,KTH Royal Institute of Technology
Journal of the Royal Society Interface | Year: 2011

Abdominal aortic aneurysms (AAAs) are frequently characterized by the development of an intra-luminal thrombus (ILT), which is known to have multiple biochemical and biomechanical implications. Development of the ILT is not well understood, and shear-stress-triggered activation of platelets could be the first step in its evolution. Vortical structures (VSs) in the flow affect platelet dynamics, which motivated the present study of a possible correlation between VS and ILT formation in AAAs. VSs educed by the λ 2- method using computational fluid dynamics simulations of the backward-facing step problem, normal aorta, fusiform AAA and saccular AAA were investigated. Patient-specific luminal geometries were reconstructed from computed tomography scans, and Newtonian and Carreau-Yasuda models were used to capture salient rheological features of blood flow. Particularly in complex flow domains, results depended on the constitutive model. VSs developed all along the normal aorta, showing that a clear correlation between VSs and high wall shear stress (WSS) existed, and that VSs started to break up during late systole. In contrast, in the fusiform AAA, large VSs developed at sites of tortuous geometry and high WSS, occupying the entire lumen, and lasting over the entire cardiac cycle. Downward motion of VSs in the AAA was in the range of a few centimetres per cardiac cycle, and with a VS burst at that location, the release (from VSs) of shear-stress-activated platelets and their deposition to the wall was within the lower part of the diseased artery, i.e. where the thickest ILT layer is typically observed. In the saccular AAA, only one VS was found near the healthy portion of the aorta, while in the aneurysmatic bulge, no VSs occurred. We present a fluid-dynamics-motivated mechanism for platelet activation, convection and deposition in AAAs that has the potential of improving our current understanding of the pathophysiology of fluid-driven ILT growth. © 2011 The Royal Society.


Shirabe T.,KTH Royal Institute of Technology
Computers, Environment and Urban Systems | Year: 2012

Map algebra is a methodology for organizing and processing digital cartographic data in a geographic information system (GIS). While its capabilities to describe patterns existing (or hidden) in data have been well studied, its capabilities to prescribe new patterns in response to specific requirements have not been much explored. The latter, prescriptive capabilities help planners address a class of spatial problems called " cartographic allocation" (. Tomlin, 1990), which concerns allocation of subsets (or zones) of a cartographic space to certain uses according to one or more criteria. Taking a school districting problem as an example, this paper introduces a systematic approach to designing a map algebraic procedure for a cartographic allocation problem with capacity constraints. It is found that a classical trial-and-error heuristic can be refined to a more formal approximation method and serve as a good alternative to other solution methods when the problem involves a large number of spatial units as is often the case with a raster-based GIS. © 2011 Elsevier Ltd.


Cvetkovic V.,KTH Royal Institute of Technology
Water Resources Research | Year: 2012

A power-law extension of the gamma distribution is proposed as a general memory function for capturing rate limitations of retention in groundwater transport. Using moments, we show how the new memory function can be reduced to most other forms available in the literature, exactly or approximately. The proposed formulation is suitable for field scale or laboratory scale transport modeling. Rate limitation effects are illustrated for solute transport by considering the fractional mass release over a given transport scale. The equilibrium and no-retention cases set bounds for contaminant attenuation, between which the impact of rate limitations is clearly exposed.


Cantoni M.,University of Melbourne | Jonsson U.T.,KTH Royal Institute of Technology | Kao C.-Y.,National Sun Yat - sen University
IEEE Transactions on Automatic Control | Year: 2012

A framework is established for directly accommodating feedback interconnections of unstable distributed-parameter transfer functions in robust stability analysis via integral quadratic constraints (IQCs). This involves transfer function homotopies that are continuous in a ν -gap metric sense. As such, the development includes the extension of ν-gap metric concepts to an irrational setting and the study of uncertainty-set connectedness in these terms. The main IQC based robust stability result is established for constantly-proper transfer functions in the Callier-Desoer algebra; i.e. finitely many unstable poles and a constant limit at infinity. Problems of structured robust stability analysis and robust performance analysis are considered to illustrate use of the main result. Several numerical examples are also presented. These include stability analysis of an autonomous system with uncertain time-delay and a closed-loop control system, accounting for both the gain and phase characteristics of the distributed-parameter uncertainty associated with the nominal rational plant model used for controller synthesis. © 2011 IEEE.


Ekener-Petersen E.,KTH Royal Institute of Technology | Finnveden G.,KTH Royal Institute of Technology
International Journal of Life Cycle Assessment | Year: 2013

Purpose: A generic hotspot assessment of social impacts from a product was conducted, using a laptop computer as a case. The aims of the case study were to identify social hotspots of the laptop and to test and evaluate the methodology. Methods: The case study was based on the social LCA methodology described in the Guidelines for social LCA and included the product system from 'cradle to grave' as well as the impacts on all relevant stakeholders. We focused on a simplified list of materials and used mainly country-specific data. Results and discussion: A new method for impact assessment of hotspots was developed. The total activity in each phase was distributed among countries. The countries were divided into groups related to the extent of activity in the product system, as well as to their performance on a subcategory. High values in both groups were highlighted and hotspots were identified. The results revealed some hotspots, some hot countries and some hot issues, all indicating a risk of negative social impacts in the product system of a laptop. It also identified workers and the local community as the stakeholders most at risk of negative social impacts. Among the hotspots identified, the following subcategories were of importance: safe and healthy living conditions, social benefit/social security, access to material resources, involvement in areas with armed conflicts, community engagement (lack of), corruption, and access to immaterial resources. Conclusions: The study showed it is possible to conduct a social LCA on a generic complex product using the Guidelines, even though data collection was impaired by lack of data and low data quality. It identified methodological issues that need further attention, for example the indicator impact pathways. Still, it is clear that new insights can be gained by social LCA, where the life cycle perspective and the systematic approach help users identify potentially important aspects that could otherwise have been neglected. © 2012 Springer-Verlag.


Ekener-Petersen E.,KTH Royal Institute of Technology | Moberg A.,KTH Royal Institute of Technology
International Journal of Life Cycle Assessment | Year: 2013

Purpose: We present experiences and reflections from social life cycle assessment (S-LCA) case study, the aim of which was to identify social hotspots, test and evaluate the methodology and propose improvements. This paper discusses the usability and applicability of the methodology used based on our experiences from the study. The main issues considered are whether the gathering of data and other information is feasible and straightforward to perform, whether the method provides added value and relevant results and how these can be presented. Method: We have conducted a generic hotspot assessment on a laptop computer according to the Guidelines for Social Life Cycle Assessment of Products (Benoît and Mazijn 2009). The experiences presented were gathered throughout the case study. The supply chain of the laptop was simplified, and we focused on a limited number of materials. The impacts were assessed in relation to the area of protection on human well-being and to affected stakeholders. Social impacts from the actual use of the product were not included. Methodological sheets were used for guidance on inventory indicators and data sources for data collection. Country-specific data were collected and entered into a spreadsheet. The process has been guided by regular meetings in a reference group, composed of representatives of all stakeholder groups. Results and discussion: The data collection process was impaired by a lack of data and low data quality. In order to relate the data collected to the product assessed, each country's share of the activity performed in each phase was determined, and the activity percentage was calculated. In order to consider and relate all the phases in the product system, we used an estimated activity variable due to the lack of data. We developed a new approach to impact assessment. By determining the combination of the most extensive activity, as well as the most negative in the range of possible values for involved countries, we identified the hotspots. The results were not further aggregated in order to promote transparency. Conclusions: We found the S-LCA methodology to be feasible and useful. By handling all relevant issues within one study using a systems perspective on the product life cycle, knowledge can be gained. However, there are still some major challenges. The definition of relevant indicators, data availability, impact pathways, activity variables, results presentation and possible aggregation, the handling of stakeholder context and the restricted assessment of the use phase were identified as major issues to deal with in further studies. Communication, and hence use of the results, is a crucial issue to enable the outcome of a study to result in actions that actually improve human well-being. © 2012 Springer-Verlag.


Sorlin S.,KTH Royal Institute of Technology | Sorlin S.,University of Stockholm
Environmental Science and Policy | Year: 2013

This article examines the concepts 'environment' and 'expertise'. It is argued that these concepts, while having long and diverse individual histories, acquired new meaning through a process of mutual co-production which occurred largely in the period 1920-1960, thus significantly preceding the common understanding of environmentalism as a phenomenon emerging in the 1960s. It is further argued that environmental expertise is much predicated on natural science in a range of fields that were integrated into a comprehensive understanding scaling upwards from the local to the global. Quantitative analysis, observing, measuring, and monitoring rates of change of a growing set of indicators were other key features of this emerging understanding of the environmental. Yet another key aspect was the self-proclaimed ability of environmental expertise to predict rates and directions of current and, crucially, future changes of global environmental conditions, increasingly assuming that these changes were largely of human origin. In addition to thus presenting a brief history of environmental expertise the article also makes the point that the environmental was, despite changed by human action, essentially regarded as something that did not in itself belong to the human or the social and thus the implicit prerogative of the natural sciences. The article argues, on the contrary, that there is solid historical evidence to suggest that 'environment' should also, perhaps primarily, be understood as a social concept, or rather as an extension of the social into nature. As conventional environmental expertise has failed to provide the advice needed to question the driving forces behind environmental degradation and lack of sustainability it is here instead suggested that environmental expertise be fundamentally reconfigured to include the social sciences and humanities, and that concerted research efforts are directed to the understanding of the formation of environmental expertise. © 2013.


Miao G.,KTH Royal Institute of Technology
IEEE Transactions on Wireless Communications | Year: 2013

This paper addresses optimal energy-efficient design for uplink (UL) MU-MIMO in a single cell environment. The energy efficiency is measured by throughput per Joule, while both RF transmission power and device electronic circuit power are considered. We define the energy efficiency (EE) capacity for UL MU-MIMO and study the power allocation that achieves this capacity. First we assume all users consume a fixed amount of circuit power and show that user antennas should be used only when the corresponding spatial channels are sufficiently good and using them improves the overall network EE. Mobile devices may have improved circuit management capability and turn off circuit operations when some antennas are not used to reduce circuit power consumption. Therefore we further study energy-efficient UL MU-MIMO with improved circuit management and show that some antennas should not be used even when their channel states are good because turning them on consumes too much circuit power. Based on theoretical analysis, we further develop low-complexity yet globally optimal energy-efficient power allocation algorithms that converge to the optimum exponentially. Simulation results are provided to demonstrate the significant gain in network energy efficiency. © 2002-2012 IEEE.


Joshi S.K.,University of Oulu | Weeraddana P.C.,KTH Royal Institute of Technology | Codreanu M.,University of Oulu | Latva-Aho M.,University of Oulu
IEEE Transactions on Signal Processing | Year: 2012

The problem of weighted sum-rate maximization (WSRMax) in multicell downlink multiple-input single-output (MISO) systems is considered. The problem is known to be NP-hard. We propose a method, based on branch and bound technique, which solves globally the nonconvex WSRMax problem with an optimality certificate. Specifically, the algorithm computes a sequence of asymptotically tight upper and lower bounds and it terminates when the difference between them falls below a pre-specified tolerance. Novel bounding techniques via conic optimization are introduced and their efficiency is demonstrated by numerical simulations. The proposed method can be used to provide performance benchmarks by back-substituting it into many existing network design problems which relies on WSRMax problem. The method proposed here can be easily extended to maximize any system performance metric that can be expressed as a Lipschitz continuous and increasing function of signal-to-interference-plus-noise ratio. © 2011 IEEE.


Katselis D.,KTH Royal Institute of Technology
IEEE Communications Letters | Year: 2012

A fundamental problem in training-based channel estimation for various communication systems is the preamble design. Two crucial aspects in such a design are the achievable mean square error (MSE) and the corresponding peak-to-average power ratio (PAPR). In this letter, preamble-based least squares (LS) channel estimation in CP-OFDM systems is considered. Ignoring the PAPR aspect, several MSE-optimal preambles and a necessary condition for their existence are presented. To this end, a training energy constraint, containing also the energy spent to the cyclic prefix (CP), is imposed. This constraint differs from the usual training energy constraints in the existing literature, which ignore the CP energy during training. These preambles contribute in the completion of existing results concerning MSE-optimal preambles in CP-OFDM systems. However, since high PAPR is an issue concerning these optimal designs, we show how these MSE-optimal preambles can be combined with the usual Zadoff-Chu (ZC) sequences to enlarge the class of PAPR-optimal preambles that achieve good MSE performance at the same time. © 2012 IEEE.


Shi G.,KTH Royal Institute of Technology | Johansson K.H.,KTH Royal Institute of Technology | Hong Y.,Chinese Academy of Sciences
IEEE Transactions on Automatic Control | Year: 2013

In this paper, multi-agent systems minimizing a sum of objective functions, where each component is only known to a particular node, is considered for continuous-time dynamics with time-varying interconnection topologies. Assuming that each node can observe a convex solution set of its optimization component, and the intersection of all such sets is nonempty, the considered optimization problem is converted to an intersection computation problem. By a simple distributed control rule, the considered multi-agent system with continuous-time dynamics achieves not only a consensus, but also an optimal agreement within the optimal solution set of the overall optimization objective. Directed and bidirectional communications are studied, respectively, and connectivity conditions are given to ensure a global optimal consensus. In this way, the corresponding intersection computation problem is solved by the proposed decentralized continuous-time algorithm. We establish several important properties of the distance functions with respect to the global optimal solution set and a class of invariant sets with the help of convex and non-smooth analysis. © 1963-2012 IEEE.


Franke U.,KTH Royal Institute of Technology
IEEE Transactions on Network and Service Management | Year: 2012

High enterprise IT service availability is a key success factor throughout many industries. While understanding of the economic importance of availability management is becoming more widespread, the implications for management of Service Level Agreements (SLAs) and thinking about availability risk management are just beginning to unfold. This paper offers a framework within which to think about availability management, highlighting the importance of variance of outage costs. The importance of variance is demonstrated using simulations on existing data sets of revenue data. An important implication is that when outage costs are proportional to outage duration, more but shorter outages should be preferred to fewer but longer, in order to minimize variance. Furthermore, two archetypal cases where the cost of an outage depends non-linearly on its duration are considered. An optimal outage length is derived, and some guidance is also given for its application when the variance of hourly downtime costs is considered. The paper is concluded with a discussion about the feasibility of the method, its practitioner relevance and its implications for SLA management. © 2011 IEEE.


Wahlberg B.,KTH Royal Institute of Technology | Hjalmarsson H.,KTH Royal Institute of Technology | Stoica P.,Uppsala University
IEEE Transactions on Automatic Control | Year: 2012

We consider the problem of minimum-variance excitation design for frequency response estimation based on finite impulse response (FIR) and output error (OE) models. The objective is to minimize the power of the input signal to be used in the system identification experiment subject to a model accuracy constraint. For FIR and OE models this leads to a finite dimensional semi-definite programming optimization problem. We study, in detail, how to apply this approach to the estimation of the frequency response at a given frequency, ω. The first case concerns minimizing the asymptotic variance of the estimated frequency response based on an FIR model estimate. We compare the optimal input signal with a sinusoidal signal with frequency ω that gives the same model accuracy, and show that the input power can, at best, be reduced by a factor of two when using the optimal input signal. Conditions are given under which the sinusoidal signal is optimal, and it is shown that this is a common case for higher order FIR models. Next, we study FIR model based estimation of the absolute value and phase of the frequency response at a given frequency, ω. We derive the corresponding optimal input signals and compare their performances with that of a sinusoidal input signal with frequency ω. The relative reduction of input power when using the optimal solution is at best a factor of two. Finally, we discuss how to extend the FIR results to OE system identification by using an input parametrization proposed by Stoica and Sderstrm (1982). © 2011 IEEE.


Svec J.G.,Palacky University | Granqvist S.,KTH Royal Institute of Technology
American Journal of Speech-Language Pathology | Year: 2010

Purpose: This tutorial addresses fundamental characteristics of microphones (frequency response, frequency range, dynamic range, and directionality), which are important for accurate measurements of voice and speech. Method: Technical and voice literature was reviewed and analyzed. The following recommendations on desirable microphone characteristics were formulated: The frequency response of microphones should be flat (i.e., variation of less than 2 dB) within the frequency range between the lowest expected fundamental frequency of voice and the highest spectral component of interest. The equivalent noise level of the microphones is recommended to be at least 15 dB lower than the sound level of the softest phonations. The upper limit of the dynamic range of the microphone should be above the sound level of the loudest phonations. Directional microphones should be placed at the distance that corresponds to their maximally flat frequency response, to avoid the proximity effect; otherwise, they will be unsuitable for spectral and level measurements. Numerical values for these recommendations were derived for the microphone distances of 30 cm and 5 cm. Conclusions: The recommendations, while preliminary and in need of further numerical justification, should provide the basis for better accuracy and repeatability of studies on voice and speech production in the future. © American Speech-Language-Hearing Association.


Littke H.,KTH Royal Institute of Technology
Urban Forestry and Urban Greening | Year: 2016

One day in 2005, a bench, some grass, and a tree suddenly appeared on a parking spot in central San Francisco. The parking meter was paid for two hours, and after that the installation disappeared. This action by the art-design-activist organization Rebar has led to the annual global event Park(ing) Day and an official planning program in San Francisco, From Pavements to Parks, inspiring cities around the world to introduce their own parklet projects.Many cities are facing challenges such as economic deficits and a lack of open public spaces, and growing concerns exist regarding the need for urban greenery. This paper discusses how parklets are challenging the role of public spaces and urban nature, drawing on discussions and conceptualizations of publicness, observational data, literature review, and document analysis to explore the influence of parklets as an urban design strategy at a local and global level.The symbolic change from parking space to public park space and the tactical urbanism inspiration of the concept constitute both parts of the symbolic value of parklets. At the same time, the line between community activism and urban strategy has been blurred. The city reviews, permits, and inspects the projects; and the sponsor is responsible for the design, financing, maintenance, and liability. The paper concludes that, even though parklets might provide a new public space and bring greenery to streetscapes, publicness, roles and responsibility, as well as the functionality of nature in these projects, remain crucial questions. © 2016 Elsevier GmbH.


Kiasari A.E.,KTH Royal Institute of Technology | Jantsch A.,KTH Royal Institute of Technology | Lu Z.,KTH Royal Institute of Technology
ACM Computing Surveys | Year: 2013

This article reviews four popular mathematical formalisms-queueing theory, network calculus, schedulability analysis, anddataflow analysis-and how they have been applied to the analysis of on-chip communication performance in Systems-on-Chip. The article discusses the basic concepts and results of each formalism and provides examples of how they have been used in Networks-on-Chip (NoCs) performance analysis. Also, the respective strengths and weaknesses of each technique and its suitability for a specific purpose are investigated. An open research issue is a unified analytical model for a comprehensive performance evaluation of NoCs. To this end, this article reviews the attempts that have been made to bridge these formalisms. © 2013 ACM.


Zhu J.,KTH Royal Institute of Technology | Birgisson B.,KTH Royal Institute of Technology | Kringos N.,KTH Royal Institute of Technology
European Polymer Journal | Year: 2014

Advances and challenges in the field of bitumen polymer modification for road construction during the last 40 years are reviewed in this paper. The history of bitumen polymer modification is described chronologically. Some popular plastomers and thermoplastic elastomers in bitumen modification are discussed regarding their advantages and disadvantages, including polyethylene (PE), polypropylene (PP), ethylene-vinyl acetate (EVA), ethylene-butyl acrylate (EBA), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS) and styrene-ethylene/butylene-styrene (SEBS). Although these polymers all improve bitumen properties to some extent, there are still some drawbacks limiting the future development of bitumen polymer modification, such as high cost, low ageing resistance and poor storage stability of polymer modified bitumen (PMB). Researchers attempted various ways to remove these drawbacks. Some technical developments for removing drawbacks are reviewed in this paper, including saturation, sulfur vulcanization, adding antioxidants, using hydrophobic clay minerals, functionalization and application of reactive polymers. The future development of polymers for bitumen modification is analyzed as well. Since it is currently challenging to perfectly achieve all expected PMB properties at the same time, some compromised recommendations are given in this paper, among which greatly enhancing the properties with an acceptably high cost, significantly reducing the cost with relatively poor properties and their combinations. Functionalization is emphasized as a promising way to enhance the properties of currently used polymers and develop new-type polymer modifiers with much greater success in the future. It is also recommended that future research on bitumen polymer modification focuses more on function development towards enhancing: Adhesion with aggregates, long-term performance and recyclability. © 2014 Elsevier Ltd. All rights reserved.


Leurent S.,Imperial College London | Volin D.,KTH Royal Institute of Technology | Volin D.,NASU Bogolyubov Institute for Theoretical Physics
Nuclear Physics B | Year: 2013

Using the FiNLIE solution of the AdS/CFT Y-system, we compute the anomalous dimension of the Konishi operator in planar N=4 SYM up to eight loops, i.e. up to the leading double wrapping order. At this order a non-reducible Euler-Zagier sum, ζ1,2,8, appears for the first time. We find that at all orders in perturbation, every spectral-dependent quantity of the Y-system is expressed through multiple Hurwitz zeta functions, hence we provide a Mathematica package to manipulate these functions, including the particular case of Euler-Zagier sums. Furthermore, we conjecture that only Euler-Zagier sums can appear in the answer for the anomalous dimension at any order in perturbation theory.We also resum the leading transcendentality terms of the anomalous dimension at all orders, obtaining a simple result in terms of Bessel functions. Finally, we demonstrate that exact Bethe equations should be related to an absence of poles condition that becomes especially non-trivial at double wrapping. © 2013 Elsevier B.V.


Schmid P.J.,Imperial College London | Brandt L.,KTH Royal Institute of Technology
Applied Mechanics Reviews | Year: 2014

This article presents techniques for the analysis of fluid systems. It adopts an optimization-based point of view, formulating common concepts such as stability and receptivity in terms of a cost functional to be optimized subject to constraints given by the governing equations. This approach differs significantly from eigenvalue-based methods that cover the time-asymptotic limit for stability problems or the resonant limit for receptivity problems. Formal substitution of the solution operator for linear time-invariant systems results in the matrix exponential norm and the resolvent norm as measures to assess the optimal response to initial conditions or external harmonic forcing. The optimization-based approach can be extended by introducing adjoint variables that enforce governing equations and constraints. This step allows the analysis of far more general fluid systems, such as time-varying and nonlinear flows, and the investigation of wavemaker regions, structural sensitivities, and passive control strategies. Copyright © 2014 by ASME.


Boano F.,Polytechnic University of Turin | Harvey J.W.,U.S. Geological Survey | Marion A.,University of Padua | Packman A.I.,Northwestern University | And 3 more authors.
Reviews of Geophysics | Year: 2014

Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed. ©2014. American Geophysical Union. All Rights Reserved.


Ohlsson T.,KTH Royal Institute of Technology | Zhang H.,Max Planck Institute for Nuclear Physics | Zhou S.,KTH Royal Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The discovery of leptonic CP violation is one of the primary goals of next-generation neutrino oscillation experiments, which is feasible due to the recent measurement of a relatively large leptonic mixing angle θ13. We suggest two new working observables ΔAαβm≡max [AαβCP(δ)]- min[AαβCP(δ)] and ΔAαβCP(δ) ≡AαβCP(δ)-AαβCP(0) to describe the CP-violating effects in long-baseline and atmospheric neutrino oscillation experiments. The former signifies the experimental sensitivity to the leptonic Dirac CP-violating phase δ and can be used to optimize the experimental setup, while the latter measures the intrinsic leptonic CP violation and can be used to extract δ directly from the experimental observations. Both analytical and numerical analyses are carried out to illustrate their main features. It turns out that an intense neutrino beam with sub-GeV energies and a baseline of a few 100 km may serve as an optimal experimental setup for probing leptonic CP violation. © 2013 American Physical Society.


Jalden J.,KTH Royal Institute of Technology | Elia P.,Eurecom
IEEE Transactions on Information Theory | Year: 2012

In the setting of quasi-static multiple-input multiple-output channels, we consider the high signal-to-noise ratio (SNR) asymptotic complexity required by the sphere decoding (SD) algorithm for decoding a large class of full-rate linear space-time codes. With SD complexity having random fluctuations induced by the random channel, noise, and codeword realizations, the introduced SD complexity exponent manages to concisely describe the computational reserves required by the SD algorithm to achieve arbitrarily close to optimal decoding performance. Bounds and exact expressions for the SD complexity exponent are obtained for the decoding of large families of codes with arbitrary performance characteristics. For the particular example of decoding the recently introduced threaded cyclic-division-algebra-based codes - the only currently known explicit designs that are uniformly optimal with respect to the diversity multiplexing tradeoff - the SD complexity exponent is shown to take a particularly concise form as a non-monotonic function of the multiplexing gain. To date, the SD complexity exponent also describes the minimum known complexity of any decoder that can provably achieve a gap to maximum likelihood performance that vanishes in the high SNR limit. © 2012 IEEE.


Meier H.,KTH Royal Institute of Technology | Wallin M.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2012

Recently, the scaling result z=d for the dynamic critical exponent at the Bose glass to superfluid quantum phase transition has been questioned both on theoretical and numerical grounds. This motivates a careful evaluation of the critical exponents in order to determine the actual value of z. We study a model of quantum bosons at T=0 with disorder in 2D using highly effective worm Monte Carlo simulations. Our data analysis is based on a finite-size scaling approach to determine the scaling of the quantum correlation time from simulation data for boson world lines. The resulting critical exponents are z=1.8±0.05, ν=1.15±0.03, and η=-0.3±0.1, hence suggesting that z=2 is not satisfied. © 2012 American Physical Society.


Manyuhina O.V.,KTH Royal Institute of Technology | Amar M.B.,Ecole Normale Superieure de Paris
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2013

We study theoretically the formation of long-wavelength instability patterns observed at spreading of nematic droplets on liquid substrates. The role of surface-like elastic terms in nematic films of submicron thickness is (re)examined by extending our previous work to hybrid aligned nematics. We identify the upper threshold for the formation of stripes and compare our results with experimental observations. We find that the wavelength and the amplitude of the in-plane director undulations can be related to the small but finite azimuthal anchoring. Within a simplified model we analyse the possibility of non-planar base state below the Barbero-Barberi critical thickness. © 2013 Elsevier B.V.


Muduli P.K.,Gothenburg University | Heinonen O.G.,Argonne National Laboratory | Heinonen O.G.,Northwestern University | Akerman J.,Gothenburg University | Akerman J.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2012

We discuss the coherence of magnetic oscillations in a magnetic tunnel junction based spin torque oscillator as a function of the external field angle. Time-frequency analysis shows mode hopping between distinct oscillator modes, which arises from linear and nonlinear couplings in the Landau-Lifshitz-Gilbert equation, analogous to mode hopping observed in semiconductor ring lasers. These couplings and, therefore, mode hopping are minimized near the current threshold for the antiparallel alignment of free-layer with reference layer magnetization. Away from the antiparallel alignment, mode hopping limits oscillator coherence. © 2012 American Physical Society.


Aurell E.,KTH Royal Institute of Technology | Aurell E.,Aalto University | Aurell E.,Albanova University Center | Ekeberg M.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2012

We show that a method based on logistic regression, using all the data, solves the inverse Ising problem far better than mean-field calculations relying only on sample pairwise correlation functions, while still computationally feasible for hundreds of nodes. The largest improvement in reconstruction occurs for strong interactions. Using two examples, a diluted Sherrington-Kirkpatrick model and a two-dimensional lattice, we also show that interaction topologies can be recovered from few samples with good accuracy and that the use of l 1 regularization is beneficial in this process, pushing inference abilities further into low-temperature regimes. © 2012 American Physical Society.


Hellman O.,Linköping University | Skorodumova N.V.,KTH Royal Institute of Technology | Skorodumova N.V.,Uppsala University | Simak S.I.,Linköping University
Physical Review Letters | Year: 2012

Charge redistribution at low oxygen vacancy concentrations in ceria have been studied in the framework of the density functional theory. We propose a model to approach the dilute limit using the results of supercell calculations. It allows one to reproduce the characteristic experimentally observed behavior of composition versus oxygen pressure dependency. We show that in the dilute limit the charge redistribution is likely to be driven by a mechanism different from the one involving electron localization on cerium atoms. We demonstrate that it can involve charge localization on light element impurities. © 2012 American Physical Society.


Wang M.,Dalian University of Technology | Han K.,Dalian University of Technology | Zhang S.,Dalian University of Technology | Sun L.,Dalian University of Technology | Sun L.,KTH Royal Institute of Technology
Coordination Chemistry Reviews | Year: 2015

The development of energy-efficient, cost-effective and durable photocatalytic systems for water splitting is one of the scientific problems that must be solved before the successful transformation from a fossil fuel-based economy to a solar fuel-based economy can be realized. Conventional photocatalytic systems are generally divided into heterogeneous systems of semiconductors, usually modified by noble metals or inorganic cocatalysts, and homogeneous systems comprised of molecular catalysts and organic or organometallic chromophores. In recent years, some hybrid photocatalytic systems were reported to be highly active and robust for photoinduced H2 production, indicating that the integration of semiconducting materials with proper molecular catalysts is an effective strategy for constructing efficient photocatalytic systems for water splitting. This review will focus on hybrid photocatalytic systems, developed in the past three years, in which proton reduction molecular catalysts incorporate either semiconducting materials or inorganic, metal-organic, and other polymeric nanomaterials for photochemical H2 generation from water. In the last section of the review, problems existing in the current hybrid photocatalytic systems are discussed; future challenges and developments are envisaged. © 2014 Elsevier B.V.


Zetterberg P.,KTH Royal Institute of Technology
Eurasip Journal on Advances in Signal Processing | Year: 2011

We describe an implementation of TDD reciprocity based zero-forcing linear precoding on a wireless testbed. A calibration technique which self-calibrates the base-station without the need for help from other nodes is described. Performance results in terms of downlink channel estimation error as well as bit error rate (BER) and signal to interference noise and distortion ratio (SINDR) are presented for a scenario with two base-stations and two mobile stations, with two antennas at the base-stations and a single antenna at the mobile-station. The results show considerable performance improvements over reference schemes (such as maximum ratio transmission). However, our analysis also reveals that the hardware impairments significantly limit the performance achieved. We further investigate how to model these impairments and attempt to predict the SINDR, such as what would be needed in a coordinated multipoint (CoMP) scenario where scheduling is performed jointly over the two cells. Although the results are obtained for a MISO scenario the general conclusions are relevant also for MIMO scenarios. Copyright © 2011 Per Zetterberg.


Abrahamsson L.,KTH Royal Institute of Technology | Soder L.,KTH Royal Institute of Technology
IEEE Transactions on Vehicular Technology | Year: 2011

Transports via rail are increasing, and major railway infrastructure investments are expected. An important part of this infrastructure is the railway power supply system (RPSS). Future railway power demands are not known. The more distant the uncertain future, the greater the number of scenarios that have to be considered. Large numbers of scenarios make time-demanding (some minutes, each) full simulations of electric railway power systems less attractive and simplifications more so. The aim, and main contribution, of this paper is to propose a fast approximator that uses aggregated traction system information as inputs and outputs. This approximator can be used as an investment planning constraint in the optimization. It considers that there is a limit on the intensity of the train traffic, depending on the strength of the power system. This approximator approach has not previously been encountered in the literature. In the numerical example of this paper, the approximator inputs are the power system configuration; the distance between a connection from contact line to the public grid, to another connection, or to the end of the contact line; the average values and the standard deviations of the inclinations of the railway; the average number of trains; and their average velocity for that distance. The output is the maximal attainable average velocity of an added train for the described railway power system section. The approximator facilitates studies of many future railway power system loading scenarios, combined with different power system configurations, for investment planning analysis. The approximator is based on neural networks. An additional value of the approximator is that it provides an understanding of the relations between power system configuration and train traffic performance. © 2010 IEEE.


Sandberg H.,KTH Royal Institute of Technology | Delvenne J.-C.,University of Namur | Doyle J.C.,California Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

In this paper, we take a control-theoretic approach to answering some standard questions in statistical mechanics, and use the results to derive limitations of classical measurements. A central problem is the relation between systems which appear macroscopically dissipative but are microscopically lossless. We show that a linear system is dissipative if, and only if, it can be approximated by a linear lossless system over arbitrarily long time intervals. Hence lossless systems are in this sense dense in dissipative systems. A linear active system can be approximated by a nonlinear lossless system that is charged with initial energy. As a by-product, we obtain mechanisms explaining the Onsager relations from time-reversible lossless approximations, and the fluctuation-dissipation theorem from uncertainty in the initial state of the lossless system. The results are applied to measurement devices and are used to quantify limits on the so-called observer effect, also called back action, which is the impact the measurement device has on the observed system. In particular, it is shown that deterministic back action can be compensated by using active elements, whereas stochastic back action is unavoidable and depends on the temperature of the measurement device. © 2006 IEEE.


Briat C.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

The Jensen's inequality plays a crucial role in the analysis of time-delay and sampled-data systems. Its conservatism is studied through the use of the Grüss Inequality. It has been reported in the literature that fragmentation (or partitioning) schemes allow to empirically improve the results. We prove here that the Jensen's gap can be made arbitrarily small provided that the order of uniform fragmentation is chosen sufficiently large. Nonuniform fragmentation schemes are also shown to speed up the convergence in certain cases. Finally, a family of bounds is characterized and a comparison with other bounds of the literature is provided. It is shown that the other bounds are equivalent to Jensen's and that they exhibit interesting well-posedness and linearity properties which can be exploited to obtain better numerical results. © 2011 IEEE.


Olsson J.,Lund University | Ryden T.,KTH Royal Institute of Technology
IEEE Transactions on Signal Processing | Year: 2011

Smoothing in state-space models amounts to computing the conditional distribution of the latent state trajectory, given observations, or expectations of functionals of the state trajectory with respect to this distribution. In recent years there has been an increased interest in Monte Carlo-based methods, often involving particle filters, for approximate smoothing in nonlinear and/or non-Gaussian state-space models. One such method is to approximate filter distributions using a particle filter and then to simulate, using backward kernels, a state trajectory backwards on the set of particles. We show that by simulating multiple realizations of the particle filter and adding a Metropolis-Hastings step, one obtains a Markov chain Monte Carlo scheme whose stationary distribution is the exact smoothing distribution. This procedure expands upon a similar one recently proposed by Andrieu, Doucet, Holenstein, and Whiteley. We also show that simulating multiple trajectories from each realization of the particle filter can be beneficial from a perspective of variance versus computation time, and illustrate this idea using two examples. © 2011 IEEE.


Ranstad P.,Alstom | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Industrial Electronics | Year: 2011

In this paper, a method to adjust the ac winding capacitance of high-voltage high-frequency transformers by means of windingrectifier integration is described. First, a theoretical background to the method is given. From the theory, an equivalent circuit describing the characteristics of the combination of the transformer and the rectifier is derived. The derived circuit introduces the concept of a dc capacitance. Finally, the equivalent circuit and the method itself are verified by means of experiments on a transformerrectifier system from an industrial application with the ratings 70 kV, 30 kW, and 25 kHz. The results from the experiments show that it is possible to vary the ac component of the winding capacitance from a few percent up to 95% of the total winding capacitance. This means that it is virtually free to choose between ac and dc capacitances during the design stage. This is very important in applications such as resonant converters with transformers having secondary windings connected to rectifiers with capacitive output filters. © 2010 IEEE.


Hjalmarsson H.,KTH Royal Institute of Technology | Martensson J.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

This paper addresses the problem of quantifying the model error (variance-error) in estimates of dynamic systems. It is shown that, under very general conditions, the asymptotic (in data length) covariance of an estimated system property (represented by a smooth function of estimated system parameters) can be interpreted in terms of an orthogonal projection of a certain function, associated with the property of interest, onto a subspace determined by the model structure and experimental conditions. The presented geometric approach simplifies structural analysis of the model variance and this is illustrated by analyzing the influence of inputs and sensors on the model accuracy. © 2011 IEEE.


Wang Y.,KTH Royal Institute of Technology | Ahlquist M.S.G.,KTH Royal Institute of Technology
Dalton Transactions | Year: 2013

Four different pathways for deprotonation of [(μ-pdt){Fe(CO) 3}{Fe(CO)(κ2-Me2PCH2N(Me) CH2PMe2)}] (pdt = propane-1,3-dithiolate) [1H μ]1+ were examined, including (1) the "Direct" deprotonation; (2) the "Indirect" deprotonation via the pendant amine N; (3) the "Indirect" deprotonation via the distal metal Fe; and (4) the "Indirect" deprotonation via the dithiolate S. Only deprotonation of the "Indirect" pathway via the pendant amine N is feasible at room temperature. The most favorable migration destination for the bridging hydride in [1Hμ]1+ is the pendant amine N (activation energy barrier 16.1 kcal mol-1). Migrations to the other two possible sites including the distal metal Fe (34.6 kcal mol-1) and the S in the dithiolate group (41.5 kcal mol-1) were hindered by high proton shuttling barriers. Once the migration barriers of those three "Indirect" pathways are overcome, the following deprotonations from all three positions including the distal atom Fe, the dithiolate S and the pendant amine N, are all feasible. The results also demonstrate a large difference for deprotonation of the hydride from the terminal and bridging sites. The low energy of the virtual orbital associated with the antibonding M-H interaction of [1HFe]1+ implies the high activity for the interaction with aniline. This journal is © The Royal Society of Chemistry 2013.


Seashore-Ludlow B.,KTH Royal Institute of Technology | Saint-Dizier F.,KTH Royal Institute of Technology | Somfai P.,Lund University | Somfai P.,University of Tartu
Organic Letters | Year: 2012

The use of asymmetric transfer hydrogenation combined with dynamic kinetic resolution for the synthesis of β-hydroxy-α-(tert-butoxycarbonyl) amino esters in water is described. This procedure provides the desired amino alcohols in good yields, diastereoselectivities, and enantioselectivities. A surfactant is employed to achieve good yields due to the hydrophobic nature of both the catalyst and substrate. The reaction setup is operationally simple, and nondegassed water can be used as the solvent. © 2012 American Chemical Society.


Yu Z.,Dalian University of Technology | Li F.,Dalian University of Technology | Sun L.,Dalian University of Technology | Sun L.,KTH Royal Institute of Technology
Energy and Environmental Science | Year: 2015

Conceptually new research on dye-sensitized photoelectrochemical cells (DS-PECs), through which solar-driven water splitting to generate solar fuel in the form of hydrogen is realized, has attracted growing interest in the past few years. DS-PECs are based on the configurations of dye-sensitized solar cells (DSCs), but with an aim to drive the two half reactions of water splitting at physically separated two compartments (electrodes) rather than to generate electrical power. Herein, we review some of the recent advances in the design and construction of functional DS-PECs for visible light-driven water splitting together with some comments on the performance of these devices. Future challenges towards the development of more efficient dye-sensitized photoelectrochemical devices are addressed in the end. © 2015 The Royal Society of Chemistry.


Pe'er A.,US Space Telescope Science Institute | Pe'er A.,Harvard - Smithsonian Center for Astrophysics | Ryde F.,KTH Royal Institute of Technology
Astrophysical Journal | Year: 2011

We consider the emission of photons from the inner parts of a relativistically expanding plasma outflow, characterized by a constant Lorentz factor, Γ. Photons that are injected in regions of high optical depth are advected with the flow until they escape at the photosphere. Due to multiple scattering below the photosphere, the locally emerging comoving photon distribution is thermal. However, as an observer simultaneously sees photons emitted from different angles, hence with different Doppler boosting, the observed spectrum is a multicolor blackbody. We calculate here the properties of the observed spectrum at different observed times. Due to the strong dependence of the photospheric radius on the angle to the line of sight, for parameters characterizing gamma-ray bursts (GRBs) thermal photons are seen up to tens of seconds following the termination of the inner engine. At late times, following the inner engine termination, both the number flux and energy flux of the thermal spectrum decay as Ft -2. At these times, the multicolor blackbody emission results in a power law at low energies (below the thermal peak), with power-law index Fνν0. We discuss the implications and limitations of this result in the study of GRBs. © 2011. The American Astronomical Society. All rights reserved.


Ullah I.,KTH Royal Institute of Technology | Parviainen P.,Aalto University | Lagergren J.,KTH Royal Institute of Technology
Molecular Biology and Evolution | Year: 2015

Species tree reconstruction has been a subject of substantial research due to its central role across biology and medicine. A species tree is often reconstructed using a set of gene trees or by directly using sequence data. In either of these cases, one of the main confounding phenomena is the discordance between a species tree and a gene tree due to evolutionary events such as duplications and losses. Probabilistic methods can resolve the discordance by coestimating gene trees and the species tree but this approach poses a scalability problem for larger data sets. We present MixTreEM-DLRS: A twophase approach for reconstructing a species tree in the presence of gene duplications and losses. In the first phase, MixTreEM, a novel structural expectation maximization algorithm based on a mixture model is used to reconstruct a set of candidate species trees, given sequence data for monocopy gene families from the genomes under study. In the second phase, PrIME-DLRS, a method based on the DLRS model (A° kerborg O, Sennblad B, Arvestad L, Lagergren J. 2009. Simultaneous Bayesian gene tree reconstruction and reconciliation analysis. Proc Natl Acad Sci USA. 106(14):5714-5719), is used for selecting the best species tree. PrIME-DLRS can handle multicopy gene families since DLRS, apart from modeling sequence evolution, models gene duplication and loss using a gene evolution model (Arvestad L, Lagergren J, Sennblad B. 2009. The gene evolution model and computing its associated probabilities. J ACM. 56(2):1-44).We evaluate MixTreEM-DLRS using synthetic and biological data, and compare its performance with a recent genome-scale species tree reconstruction method PHYLDOG (Boussau B, Sz öllosi GJ, Duret L, Gouy M, Tannier E, Daubin V. 2013. Genomescale coestimation of species and gene trees. Genome Res. 23(2):323-330) as well as with a fast parsimony-based algorithm Duptree (Wehe A, Bansal MS, Burleigh JG, Eulenstein O. 2008. Duptree: a program for large-scale phylogenetic analyses using gene tree parsimony. Bioinformatics 24(13):1540-1541). Our method is competitive with PHYLDOG in terms of accuracy and runs significantly faster and our method outperforms Duptree in accuracy. The analysis constituted by MixTreEM without DLRS may also be used for selecting the target species tree, yielding a fast and yet accurate algorithm for larger data sets. MixTreEM is freely available at http://prime. scilifelab.se/mixtreem/. © 2015 The Author.


Marboe C.,Trinity College Dublin | Volin D.,Trinity College Dublin | Volin D.,KTH Royal Institute of Technology | Volin D.,NASU Bogolyubov Institute for Theoretical Physics
Nuclear Physics B | Year: 2015

An iterative procedure perturbatively solving the quantum spectral curve of planar N=4 SYM for any operator in the sl(2) sector is presented. A Mathematica notebook executing this procedure is enclosed. The obtained results include 10-loop computations of the conformal dimensions of more than ten different operators. We prove that the conformal dimensions are always expressed, at any loop order, in terms of multiple zeta-values with coefficients from an algebraic number field determined by the one-loop Baxter equation. We observe that all the perturbative results that were computed explicitly are given in terms of a smaller algebra: single-valued multiple zeta-values times the algebraic numbers. © 2015 The Authors.


Huang L.,KTH Royal Institute of Technology | Mao X.,University of Strathclyde
IEEE Transactions on Automatic Control | Year: 2011

In recent years, singular hybrid systems have received considerable attention. However, few results are concerned with stability of singular hybrid stochastic systems. Based on a stability result for singular hybrid systems, this note studies mean-square stability of singular hybrid stochastic systems. It is found that the diffusions and the Markov chain may play important roles in system analysis in mean-square sense. As a special case, a criterion for mean-square stability of hybrid stochastic systems is developed by the frequency domain approach. © 2006 IEEE.


Chen G.,State University of New York at Buffalo | Chen G.,Harbin Institute of Technology | Agren H.,KTH Royal Institute of Technology | Ohulchanskyy T.Y.,State University of New York at Buffalo | And 2 more authors.
Chemical Society Reviews | Year: 2015

Light upconverting nanostructures employing lanthanide ions constitute an emerging research field recognized with wide ramifications and impact in many areas ranging from healthcare, to energy and, to security. The core-shell design of these nanostructures allows us to deliberately introduce a hierarchy of electronic energy states, thus providing unprecedented opportunities to manipulate the electronic excitation, energy transfer and upconverted emissions. The core-shell morphology also causes the suppression of quenching mechanisms to produce efficient upconversion emission for biophotonic and photonic applications. Using hierarchical architect, whereby each shell layer can be defined to have a specific feature, the electronic structure as well as the physiochemical structure of the upconverting nanomaterials can be tuned to couple other electronic states on the surface such as excitations of organic dye molecules or localized surface plasmons from metallic nanostructures, or to introduce a broad range of imaging or therapeutic modalities into a single conduct. In this review, we summarize the key aspects of nanophotonic control of the light upconverting nanoparticles through governed design and preparation of hierarchical shells in the core-shell nanostructures, and review their emerging applications in the biomedical field, solar energy conversion, as well as security encoding. This journal is © The Royal Society of Chemistry.


He S.,Zhejiang University | He S.,KTH Royal Institute of Technology | Zhang X.,Zhejiang University | He Y.,Zhejiang University
Optics Express | Year: 2013

Electronics circuits keep shrinking in dimensions, as requested by Moore's law. In contrast, photonic waveguides and circuit elements still have lateral dimensions on the order of the wavelength. A key to make photonics have a microelectronics-like development is a drastic reduction of size. To achieve this, we need a low-loss nanoscale waveguide with a drastically reduced mode area and an ultra-high effective refractive index. For this purpose, we propose here several low-loss waveguide structures based on graphene nano-ribbons. An extremely small mode area (∼10-7λ0 2, one order smaller than the smallest mode area of any waveguide that has ever been reported in the literature; here λ0 is the operating wavelength in vacuum) and an extremely large effective refractive index (several hundreds) are achieved. As a device example, a nano-ring cavity of ultrasmall size (with a diameter of ∼10-2λ0) is designed. Our study paves the way for future VLSI (very-large-scale integration) optoelectronics. © 2013 Optical Society of America.


Ulker-Kaustell M.,KTH Royal Institute of Technology | Karoumi R.,KTH Royal Institute of Technology
Engineering Structures | Year: 2012

Previous experimental work has identified variations in the natural frequency and the modal damping ratio of the first vertical bending mode of vibration of a simply supported, single span steel-concrete composite bridge. It was found that the natural frequency decreased and the modal damping ratio increased with increasing amplitudes of vibration. This paper illustrates the influence of these variations on the train-bridge resonance of this particular bridge by means of a non-linear single degree of freedom system, based on the previously mentioned experimental results. As one might expect, the results indicate that the influence of the increasing damping ratio leads to a considerable decrease in the resonant amplitude whilst the decreasing natural frequency decreases the critical train speed at which resonance occurs. Further studies along this line of research may help us reduce the uncertainties in dynamic assessments of existing bridges based on dynamic measurements and improve our understanding of the dynamic properties of railway bridges in general. © 2012 Elsevier Ltd.


Chiu J.N.W.,KTH Royal Institute of Technology | Gravoille P.,National Institute of Energy Hydraulic and Environmental Engineering | Martin V.,KTH Royal Institute of Technology
Applied Energy | Year: 2013

Latent heat thermal energy storage (LHTES) integrated active free cooling stores night time cold and serves as heat sink for cooling when demand rises. Passive buildings, albeit their advantages in limiting heat loss during winter time, are often paired with excessive internal overheating in summer, as shown in the first part of this study. Under the climate condition in Stockholm, LHTES systems may provide solutions for sustainable cooling with use of renewable cooling sources. This study presents a multi-objective optimization on system cost and cooling supply for various LHTES configurations followed with a sensitivity analysis on phase change material cost and energy price. Results indicate that optimized LHTES may meet cooling needs while retaining economic viability. However, LHTES based cooling systems may require substantially higher electricity demand than conventional air conditioning unit for applications where high cooling thermal power rate is to be met, a tradeoff to indoor comfort level needs to be considered to reach the concept of sustainable free cooling. We here provide a novel techno-economic feasibility study of active free cooling LHTES in Stockholm as well as new insights to cost, comfort level and energy requirement with use of multi-objective optimization algorithm. © 2013 Elsevier Ltd.


Shames I.,KTH Royal Institute of Technology | Dasgupta S.,University of Iowa | Fidan B.,University of Waterloo | Anderson B.D.O.,Australian National University
IEEE Transactions on Automatic Control | Year: 2012

Consider an agent A at an unknown location, undergoing sufficiently slow drift, and a mobile agent B that must move to the vicinity of and then circumnavigate A at a prescribed distance from A. In doing so, B can only measure its distance from A, and knows its own position in some reference frame. This paper considers this problem, which has applications to surveillance and orbit maintenance. In many of these applications it is difficult for B to directly sense the location of A, e.g. when all that B can sense is the intensity of a signal emitted by A. This intensity does, however provide a measure of the distance. We propose a nonlinear periodic continuous time control law that achieves the objective using this distance measurement. Fundamentally, a) B must exploit its motion to estimate the location of A, and b) use its best instantaneous estimate of where A resides, to move itself to achieve the circumnavigation objective. For a) we use an open loop algorithm formulated by us in an earlier paper. The key challenge tackled in this paper is to design a control law that closes the loop by marrrying the two goals. As long as the initial estimate of the source location is not coincident with the intial position of B, the algorithm is guaranteed to be exponentially convergent when A is stationary. Under the same condition, we establish that when A drifts with a sufficiently small, unknown velocity, B globally achieves its circumnavigation objective, to within a margin proportional to the drift velocity. © 2011 IEEE.


Rabkowski J.,KTH Royal Institute of Technology | Peftitsis D.,KTH Royal Institute of Technology | Nee H.-P.,KTH Royal Institute of Technology
IEEE Industrial Electronics Magazine | Year: 2012

During recent years, silicon carbide (SiC) power electronics has gone from being a promising future technology to being a potent alternative to state-of-the-art silicon (Si) technology in high-efficiency, highfrequency, and high-temperature applications. The reasons for this are that SiC power electronics may have higher voltage ratings, lower voltage drops, higher maximum temperatures, and higher thermal conductivities. It is now a fact that several manufacturers are capable of developing and processing high-quality transistors at cost that permit introduction of new products in application areas where the benefits of the SiC technology can provide significant system advantages. © 2011 IEEE.


Sou K.C.,KTH Royal Institute of Technology | Rantzer A.,Lund University
Automatica | Year: 2012

In this paper a controller reduction method for discrete-time linear time-invariant systems is described. Using the bounded-real lemma, the proposed method generates reduced controllers with closed loop stability and H∞ norm performance guarantee. Information of the full controller is used as a basis for reduction using singular value decomposition. This is different from traditional model reduction schemes such as weighted balanced truncation. Numerical assessment of the proposed method is given in the end of the paper. © 2012 Elsevier Ltd. All rights reserved.


Holzapfel G.A.,Graz University of Technology | Holzapfel G.A.,KTH Royal Institute of Technology | Ogden R.W.,University of Glasgow
Journal of the Royal Society Interface | Year: 2010

This paper provides the first analysis of the three-dimensional state of residual stress and stretch in an artery wall consisting of three layers (intima, media and adventitia), modelled as a circular cylindrical tube. The analysis is based on experimental results